diff --git a/crates/ide-host/src/lib.rs b/crates/ide-host/src/lib.rs
index 56147fcf5..2244cd7a4 100644
--- a/crates/ide-host/src/lib.rs
+++ b/crates/ide-host/src/lib.rs
@@ -223,6 +223,7 @@ impl Host {
             self.cancel_request(request);
         }
         let project = self.projects.write().remove(window)?;
+        project.plugin_diagnostics.close();
         if let Some(plugins) = plugins::editor_plugin_host() {
             plugins.invalidate_client_navigation(&project.root, Some(window), None);
             plugins.set_active_file(window, None);
@@ -373,6 +374,7 @@ impl Host {
         self.terminals.kill_all();
         let projects: Vec<_> = self.projects.write().drain().map(|(_, p)| p).collect();
         for project in &projects {
+            project.plugin_diagnostics.close();
             if let Some(bridge) = &project.kotlin_bridge {
                 bridge.stop();
             }
diff --git a/crates/ide-host/src/plugins/diagnostics.rs b/crates/ide-host/src/plugins/diagnostics.rs
new file mode 100644
index 000000000..14470f56a
--- /dev/null
+++ b/crates/ide-host/src/plugins/diagnostics.rs
@@ -0,0 +1,245 @@
+//! Versioned, project-scoped diagnostics for unsaved editor buffers.
+use super::{PluginHost, ProviderKind, editor_plugin_host};
+use ide_core::{CancellationToken, Diagnostic, DocId, IdeEvent, SharedSink};
+use ide_plugin::ProviderDocument;
+use ide_text::AppliedChange;
+use ide_workspace::documents::DocumentObserver;
+use ide_workspace::{DocumentInfo, Documents};
+use parking_lot::Mutex;
+use std::collections::{HashMap, HashSet};
+use std::path::Path;
+use std::sync::{Arc, Weak};
+use std::time::Duration;
+
+const DEBOUNCE: Duration = Duration::from_millis(300);
+
+struct Document {
+    snapshot: ProviderDocument,
+    cancel: CancellationToken,
+    sources: HashSet<String>,
+}
+
+#[derive(Default)]
+pub(super) struct State {
+    closed: bool,
+    documents: HashMap<DocId, Document>,
+    generations: HashMap<String, u64>,
+}
+
+/// One incarnation of one project's documents, shared by all its editors.
+pub(crate) struct Diagnostics {
+    state: Arc<Mutex<State>>,
+    sink: SharedSink,
+    runtime: tokio::runtime::Handle,
+    documents: Weak<Documents>,
+    root: std::path::PathBuf,
+}
+
+impl Diagnostics {
+    pub fn new(
+        sink: SharedSink,
+        runtime: tokio::runtime::Handle,
+        documents: &Arc<Documents>,
+        root: &Path,
+    ) -> Arc<Self> {
+        Arc::new(Self {
+            state: Arc::default(),
+            sink,
+            runtime,
+            documents: Arc::downgrade(documents),
+            root: root.to_path_buf(),
+        })
+    }
+
+    fn emit(&self, path: &Path, plugin: &str, items: Vec<Diagnostic>) {
+        self.sink.emit(IdeEvent::Diagnostics {
+            path: path.to_path_buf().into(),
+            source: format!("plugin-provider:{plugin}"),
+            items,
+        });
+    }
+
+    fn clear_document(&self, doc: &Document) {
+        doc.cancel.cancel();
+        for plugin in &doc.sources {
+            self.emit(&doc.snapshot.path, plugin, Vec::new());
+        }
+    }
+
+    pub fn close(&self) {
+        let mut state = self.state.lock();
+        state.closed = true;
+        for (_, doc) in state.documents.drain() {
+            self.clear_document(&doc);
+        }
+    }
+
+    fn schedule(&self, id: DocId, state: &mut State) {
+        let Some(doc) = state.documents.get_mut(&id) else { return };
+        doc.cancel.cancel();
+        doc.cancel = CancellationToken::new();
+        let Some(host) = editor_plugin_host() else { return };
+        if host.providers.plugins_for(ProviderKind::Diagnostics, &doc.snapshot.language).is_empty() {
+            return;
+        }
+        // Register only once per project incarnation; no project is retained by the host.
+        let weak = Arc::downgrade(&self.state);
+        {
+            let mut projects = host.diagnostic_projects.lock();
+            projects.retain(|(state, _)| state.strong_count() > 0);
+            if !projects.iter().any(|(state, _)| state.ptr_eq(&weak)) {
+                projects.push((weak.clone(), self.sink.clone()));
+            }
+        }
+        let root = self.root.clone();
+        let (mut snapshot, cancel, sink, documents) =
+            (doc.snapshot.clone(), doc.cancel.clone(), self.sink.clone(), self.documents.clone());
+        let lifecycle_generations = state.generations.clone();
+        self.runtime.spawn(async move {
+            tokio::time::sleep(DEBOUNCE).await;
+            if cancel.is_cancelled() || weak.strong_count() == 0 {
+                return;
+            }
+            let _ = tokio::task::spawn_blocking(move || {
+                let Some(documents) = documents.upgrade() else { return };
+                let Ok(current) = documents.snapshot(id) else { return };
+                if u64::from(current.version) != snapshot.version
+                    || current.path.0 != snapshot.path
+                    || current.language.as_str() != snapshot.language
+                    || cancel.is_cancelled()
+                {
+                    return;
+                }
+                snapshot.text = current.text;
+                drop(documents);
+
+                let generations = host.providers.diagnostic_generations(&snapshot.language);
+                let results = if snapshot.text.len() <= super::navigation::MAX_DOCUMENT_BYTES {
+                    host.provide_project_diagnostics(Some(&root), &snapshot, &cancel)
+                } else {
+                    Vec::new()
+                };
+                let Some(state) = weak.upgrade() else { return };
+                let mut state = state.lock();
+                if state.closed || cancel.is_cancelled() {
+                    return;
+                }
+                let matching: HashSet<_> = host
+                    .diagnostic_plugins(Some(&root), &snapshot.language)
+                    .into_iter()
+                    .map(|p| p.id().to_owned())
+                    .filter(|p| lifecycle_generations.get(p) == state.generations.get(p))
+                    .collect();
+                let latest = host.providers.diagnostic_generations(&snapshot.language);
+                let Some(doc) = state.documents.get_mut(&id) else { return };
+                if doc.snapshot.version != snapshot.version || doc.snapshot.path != snapshot.path {
+                    return;
+                }
+                let mut current = HashSet::new();
+                for (plugin, items) in results {
+                    if !matching.contains(&plugin)
+                        || !generations.get(&plugin).is_some_and(|seq| latest.get(&plugin) == Some(seq))
+                    {
+                        continue;
+                    }
+                    current.insert(plugin.clone());
+                    sink.emit(IdeEvent::Diagnostics {
+                        path: snapshot.path.clone().into(),
+                        source: format!("plugin-provider:{plugin}"),
+                        items,
+                    });
+                }
+                for plugin in doc.sources.difference(&current) {
+                    sink.emit(IdeEvent::Diagnostics {
+                        path: snapshot.path.clone().into(),
+                        source: format!("plugin-provider:{plugin}"),
+                        items: Vec::new(),
+                    });
+                }
+                doc.sources = current;
+            })
+            .await;
+        });
+    }
+}
+
+impl DocumentObserver for Diagnostics {
+    fn opened(&self, info: &DocumentInfo) {
+        let mut state = self.state.lock();
+        if state.closed {
+            return;
+        }
+        if let Some(old) = state.documents.remove(&info.id) {
+            self.clear_document(&old);
+        }
+        if info.large || info.uri.is_some() {
+            return;
+        }
+        state.documents.insert(
+            info.id,
+            Document {
+                snapshot: ProviderDocument {
+                    path: info.path.0.clone(),
+                    language: info.language.to_string(),
+                    version: u64::from(info.version),
+                    text: String::new(),
+                },
+                cancel: CancellationToken::new(),
+                sources: HashSet::new(),
+            },
+        );
+        self.schedule(info.id, &mut state);
+    }
+
+    fn changed(&self, id: DocId, path: &Path, version: u32, _: &[AppliedChange], _text: &dyn Fn() -> String) {
+        let mut state = self.state.lock();
+        if state.closed {
+            return;
+        }
+        let Some(doc) = state.documents.get_mut(&id) else { return };
+        if doc.snapshot.path != path {
+            self.clear_document(doc);
+            doc.sources.clear();
+        }
+        doc.snapshot.path = path.to_path_buf();
+        doc.snapshot.version = u64::from(version);
+        self.schedule(id, &mut state);
+    }
+
+    fn closed(&self, id: DocId, _: &Path) {
+        if let Some(doc) = self.state.lock().documents.remove(&id) {
+            self.clear_document(&doc);
+        }
+    }
+}
+
+impl Drop for Diagnostics {
+    fn drop(&mut self) {
+        self.close();
+    }
+}
+
+pub(super) type ProjectState = (Weak<Mutex<State>>, SharedSink);
+
+impl PluginHost {
+    pub(super) fn clear_provider_diagnostics(&self, plugin: &str) {
+        // Clone before taking a project's state lock (edits register in the other order).
+        let projects = self.diagnostic_projects.lock().clone();
+        for (state, sink) in projects {
+            if let Some(state) = state.upgrade() {
+                let mut state = state.lock();
+                // A completed answer can still be waiting for another provider.
+                *state.generations.entry(plugin.to_owned()).or_default() += 1;
+                for doc in state.documents.values_mut() {
+                    if doc.sources.remove(plugin) {
+                        sink.emit(IdeEvent::Diagnostics {
+                            path: doc.snapshot.path.clone().into(),
+                            source: format!("plugin-provider:{plugin}"),
+                            items: Vec::new(),
+                        });
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/crates/ide-host/src/plugins/mod.rs b/crates/ide-host/src/plugins/mod.rs
index e83aadb03..ad113fd45 100644
--- a/crates/ide-host/src/plugins/mod.rs
+++ b/crates/ide-host/src/plugins/mod.rs
@@ -17,6 +17,7 @@
 
 mod api;
 pub mod commit;
+pub(crate) mod diagnostics;
 pub mod endpoints;
 mod event_paths;
 mod hover;
@@ -327,6 +328,7 @@ pub struct PluginHost {
     navigation: Mutex<navigation::NavigationIndex>,
     endpoints: Mutex<endpoints::Endpoints>,
     web_ptys: Mutex<BTreeMap<String, Vec<web::WebPtySession>>>,
+    diagnostic_projects: Mutex<Vec<diagnostics::ProjectState>>,
     /// Validated UI declarations of installed packages (start-up reuses them).
     index: Arc<ContributionIndex>,
     ledger: Mutex<Ledger>,
@@ -419,6 +421,7 @@ impl PluginHost {
             navigation: Mutex::default(),
             endpoints: Mutex::default(),
             web_ptys: Mutex::default(),
+            diagnostic_projects: Mutex::default(),
             index,
             plugins: RwLock::default(),
             state: Mutex::new(state),
@@ -1942,6 +1945,7 @@ impl PluginHost {
     /// whose activation event already fired.
     fn start(&self, plugin: &Arc<LoadedPlugin>) {
         self.registry.dispose_plugin(plugin.id());
+        self.clear_provider_diagnostics(plugin.id());
         if plugin.source == PluginSource::Installed
             && let Some(reason) = self.revoked_reason(plugin.id(), &plugin.manifest().version, plugin.dir())
         {
@@ -2124,6 +2128,7 @@ impl PluginHost {
     /// A trap dropped the plugin's instance: restart it on next use after a
     /// backoff, or stop it for the session after too many crashes in a row.
     fn crashed(&self, plugin: &LoadedPlugin, error: &str, client: Option<&str>) {
+        self.clear_provider_diagnostics(plugin.id());
         let failures = {
             let mut meta = plugin.meta.lock();
             meta.failures += 1;
@@ -2191,6 +2196,7 @@ impl PluginHost {
             actor.stop(true);
         }
         self.registry.dispose_plugin(plugin.id());
+        self.clear_provider_diagnostics(plugin.id());
         self.shared.clear_plugin(plugin.id(), true);
         self.queues.lock().retain(|(id, _), _| id != plugin.id());
     }
@@ -2200,6 +2206,7 @@ impl PluginHost {
         self.clear_plugin_endpoints(plugin.id());
         tracing::warn!(plugin = %plugin.id(), "{error}");
         self.registry.dispose_plugin(plugin.id());
+        self.clear_provider_diagnostics(plugin.id());
         let mut meta = plugin.meta.lock();
         meta.status = PluginStatus::Failed;
         meta.error = Some(error);
@@ -2568,6 +2575,70 @@ impl ide_language::ExternalSyntax for PluginSyntax {
 mod tests {
     use super::*;
 
+    #[test]
+    fn host_panics_stop_actor_and_reply_on_every_call_path() {
+        let tmp = tempfile::tempdir().unwrap();
+        let host =
+            PluginHost::new(tmp.path().join("plugins"), Arc::new(|_: Option<&str>, _| {}), Limits::default()).unwrap();
+        let fixture = Path::new(env!("CARGO_MANIFEST_DIR")).join("../ide-plugin/tests/fixtures/diagnostics");
+        host.install_from_dir(&fixture, &Consent::all()).unwrap();
+        let plugin = host.get("test.diagnostics").unwrap();
+        for mode in 0..5 {
+            let (actor, _) = host.ensure_active(&plugin, None).unwrap();
+            let cancel = ide_core::CancellationToken::new();
+            let next_actor = actor.clone();
+            let (queued_tx, queued_rx) = std::sync::mpsc::channel();
+            let panic = move |_: &mut Runtime| -> Result<(), CallError> {
+                let pending = next_actor.submit(None, |_| Ok("must not run")).unwrap();
+                queued_tx.send(pending).unwrap();
+                panic!("host call panic")
+            };
+            let result = match mode {
+                0 => actor.call(None, panic),
+                1 => actor.call_cancellable(&cancel, Duration::ZERO, panic),
+                2 => actor.call_edit_cancellable(&cancel, Duration::ZERO, Duration::from_secs(5), panic),
+                _ => {
+                    let (tx, rx) = std::sync::mpsc::channel();
+                    if mode == 3 {
+                        actor.post(panic, move |result| {
+                            let _ = tx.send(result);
+                        });
+                    } else {
+                        actor.post(
+                            |_| Ok(()),
+                            move |result| {
+                                let _ = tx.send(result);
+                                panic!("completion callback panic");
+                            },
+                        );
+                    }
+                    rx.recv_timeout(Duration::from_secs(5)).expect("actor must reply")
+                }
+            };
+            if mode < 4 {
+                let queued = queued_rx.recv_timeout(Duration::from_secs(5)).unwrap();
+                assert!(matches!(queued.wait(), Err(ActorError::Stopped)), "poisoned runtime must not run queued work");
+            }
+            actor.stop(true);
+            if mode < 4 {
+                assert!(
+                    matches!(result, Err(ActorError::Call(CallError::Trap(ref message))) if message.contains("host call panic")),
+                    "{result:?}"
+                );
+            }
+            assert!(!actor.is_alive());
+            assert!(!actor.is_busy());
+            assert!(matches!(actor.call(None, |_| Ok(())), Err(ActorError::Stopped)));
+            let crash = actor.take_crash().expect("supervisor must see the panic");
+            assert!(crash.contains(if mode == 4 { "completion callback panic" } else { "host call panic" }));
+            assert!(actor.take_crash().is_none());
+            cancel.cancel();
+            // Re-enable to reset the supervisor before testing the next call path.
+            host.set_enabled("test.diagnostics", false).unwrap();
+            host.set_enabled("test.diagnostics", true).unwrap();
+        }
+    }
+
     #[test]
     fn globs() {
         assert!(glob_match("**/*Mapper.xml", "src/main/UserMapper.xml"));
diff --git a/crates/ide-host/src/plugins/providers.rs b/crates/ide-host/src/plugins/providers.rs
index ea7ceacd3..ad1d590f9 100644
--- a/crates/ide-host/src/plugins/providers.rs
+++ b/crates/ide-host/src/plugins/providers.rs
@@ -22,6 +22,7 @@
 use ide_extension::{Disposable, ExtensionPoint, Package, Placement, Prepared, UiDecl, decode, validate_item_id};
 use parking_lot::RwLock;
 use serde::{Deserialize, Serialize};
+use std::collections::{HashMap, HashSet};
 use std::sync::Arc;
 use std::sync::atomic::{AtomicU64, Ordering};
 
@@ -40,6 +41,7 @@ pub enum ProviderKind {
     SemanticTokens,
     Hover,
     InlayHints,
+    Diagnostics,
 }
 
 #[derive(Clone, Debug, Deserialize)]
@@ -73,13 +75,26 @@ impl Providers {
 
     /// Plugins providing `kind` for `language`, in declaration order.
     pub fn plugins_for(&self, kind: ProviderKind, language: &str) -> Vec<String> {
-        let mut out: Vec<String> = Vec::new();
-        for (_, plugin, kinds, languages) in self.items.read().iter() {
-            if kinds.contains(&kind) && languages.iter().any(|l| l == "*" || l == language) && !out.contains(plugin) {
-                out.push(plugin.clone());
-            }
-        }
-        out
+        self.matching::<Vec<_>>(kind, language).into_iter().map(|(plugin, _)| plugin).collect()
+    }
+
+    /// One coherent declaration snapshot, preserving the first match per plugin.
+    fn matching<T: FromIterator<(String, u64)>>(&self, kind: ProviderKind, language: &str) -> T {
+        let items = self.items.read();
+        let mut seen = HashSet::new();
+        items
+            .iter()
+            .filter(|(_, plugin, kinds, languages)| {
+                kinds.contains(&kind)
+                    && languages.iter().any(|l| l == "*" || l == language)
+                    && seen.insert(plugin.as_str())
+            })
+            .map(|(seq, plugin, ..)| (plugin.clone(), *seq))
+            .collect()
+    }
+
+    pub(super) fn diagnostic_generations(&self, language: &str) -> HashMap<String, u64> {
+        self.matching(ProviderKind::Diagnostics, language)
     }
 
     /// Whether any plugin provides `kind` (for any language).
@@ -118,6 +133,9 @@ impl ExtensionPoint for ProvidersPoint {
         if d.kinds.contains(&ProviderKind::SemanticTokens) {
             pkg.manifest.needs_api("contributes.providers: semantic-tokens", 3)?;
         }
+        if d.kinds.contains(&ProviderKind::Diagnostics) {
+            pkg.manifest.needs_api("contributes.providers: diagnostics", 3)?;
+        }
         if d.kinds.contains(&ProviderKind::Hover) {
             pkg.manifest.needs_api("contributes.providers: hover", 3)?;
         }
@@ -202,7 +220,7 @@ pub(crate) fn editor_plugin_host() -> Option<Arc<PluginHost>> {
 
 impl PluginHost {
     /// Usable plugins declaring `kind` for `language`.
-    fn provider_plugins(&self, kind: ProviderKind, language: &str) -> Vec<Arc<LoadedPlugin>> {
+    pub(super) fn provider_plugins(&self, kind: ProviderKind, language: &str) -> Vec<Arc<LoadedPlugin>> {
         self.providers
             .plugins_for(kind, language)
             .into_iter()
@@ -360,6 +378,59 @@ impl PluginHost {
         .collect()
     }
 
+    pub fn provide_diagnostics(
+        &self,
+        doc: &ProviderDocument,
+        cancel: &CancellationToken,
+    ) -> Vec<(String, Vec<ide_core::Diagnostic>)> {
+        self.provide_project_diagnostics(None, doc, cancel)
+    }
+
+    pub(super) fn diagnostic_plugins(
+        &self,
+        project: Option<&std::path::Path>,
+        language: &str,
+    ) -> Vec<Arc<LoadedPlugin>> {
+        self.provider_plugins(ProviderKind::Diagnostics, language)
+            .into_iter()
+            .filter(|p| p.dev_root.is_none() || p.dev_root.as_deref() == project)
+            .collect()
+    }
+
+    pub(super) fn provide_project_diagnostics(
+        &self,
+        project: Option<&std::path::Path>,
+        doc: &ProviderDocument,
+        cancel: &CancellationToken,
+    ) -> Vec<(String, Vec<ide_core::Diagnostic>)> {
+        std::thread::scope(|scope| {
+            let calls: Vec<_> = self
+                .diagnostic_plugins(project, &doc.language)
+                .into_iter()
+                .map(|p| {
+                    scope.spawn(move || {
+                        if cancel.is_cancelled() {
+                            return None;
+                        }
+                        let (actor, activated) = self.ensure_active(&p, None).ok()?;
+                        if activated {
+                            self.changed();
+                        }
+                        let (d, timeout) = (doc.clone(), self.limits.edit_hard);
+                        let started = Instant::now();
+                        let result =
+                            actor.call_edit_cancellable(cancel, CANCEL_GRACE, self.limits.edit_soft, move |rt| {
+                                rt.provide_diagnostics(&d, timeout)
+                            });
+                        let items = self.finish_provider_call(&p, &actor, started, result)?;
+                        (!cancel.is_cancelled()).then(|| (p.id().to_owned(), items))
+                    })
+                })
+                .collect();
+            calls.into_iter().filter_map(|call| call.join().ok().flatten()).collect()
+        })
+    }
+
     pub fn provide_hover(&self, doc: &ProviderDocument, at: ide_core::Pos) -> Vec<PluginHover> {
         let d = Arc::new(doc.clone());
         self.edit_calls(ProviderKind::Hover, &doc.language, move |rt, timeout| rt.provide_hover(&d, at, timeout))
@@ -406,3 +477,41 @@ impl PluginHost {
         None
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn provider_snapshots_preserve_order_first_generation_and_language_matching() {
+        let providers = Arc::new(Providers::default());
+        let declare = |plugin: &str, kind, language: &str| {
+            providers.add(plugin.into(), Decl { kinds: vec![kind], languages: vec![language.into()] })
+        };
+        let mut declarations = Vec::new();
+        declarations.push(declare("unrelated", ProviderKind::Hover, "*"));
+        declarations.push(declare("other-language", ProviderKind::Diagnostics, "rust"));
+        for i in 0..256 {
+            let plugin = format!("plugin-{i}");
+            declarations.push(declare(&plugin, ProviderKind::Diagnostics, "text"));
+            declarations.push(declare(&plugin, ProviderKind::Diagnostics, "*"));
+        }
+        let expected: Vec<_> = (0..256).map(|i| format!("plugin-{i}")).collect();
+        assert_eq!(providers.plugins_for(ProviderKind::Diagnostics, "text"), expected);
+        let before = providers.diagnostic_generations("text");
+        assert_eq!(before.len(), 256);
+        assert_eq!(before["plugin-0"], 2);
+        assert_eq!(providers.diagnostic_generations("rust").len(), 257);
+        assert_eq!(providers.plugins_for(ProviderKind::Hover, "text"), ["unrelated"]);
+        // Removing the first matching declaration must invalidate its generation,
+        // even while a second declaration still provides the same language.
+        drop(declarations.remove(2));
+        let after = providers.diagnostic_generations("text");
+        assert_eq!(after["plugin-0"], 3);
+        assert_ne!(before["plugin-0"], after["plugin-0"]);
+        drop(declarations);
+        assert!(providers.diagnostic_generations("text").is_empty());
+        let _reloaded = declare("plugin-0", ProviderKind::Diagnostics, "text");
+        assert_ne!(providers.diagnostic_generations("text")["plugin-0"], after["plugin-0"]);
+    }
+}
diff --git a/crates/ide-host/src/project.rs b/crates/ide-host/src/project.rs
index 92e1485e2..f99b4ff5e 100644
--- a/crates/ide-host/src/project.rs
+++ b/crates/ide-host/src/project.rs
@@ -27,6 +27,7 @@ pub struct Project {
     pub languages: Arc<LanguageRegistry>,
     pub settings: Arc<SettingsStore>,
     pub documents: Arc<Documents>,
+    pub(crate) plugin_diagnostics: Arc<crate::plugins::diagnostics::Diagnostics>,
     pub history: Arc<LocalHistory>,
     /// Undo stack of file move / rename refactorings.
     pub moves: FileMoves,
@@ -519,7 +520,11 @@ impl Host {
             sink.clone(),
         );
         ide_agent::registry::maintain(crate::ops::agent::registry_paths(self));
+        let plugin_diagnostics =
+            crate::plugins::diagnostics::Diagnostics::new(sink.clone(), self.runtime.clone(), &documents, &root);
+        documents.add_observer(plugin_diagnostics.clone());
         let project = Arc::new(Project {
+            plugin_diagnostics,
             trusted,
             root,
             sink,
@@ -665,7 +670,11 @@ impl Host {
             self.local_data_dir.join("notebook-runtime").join(uuid::Uuid::new_v4().to_string()),
             sink.clone(),
         );
+        let plugin_diagnostics =
+            crate::plugins::diagnostics::Diagnostics::new(sink.clone(), self.runtime.clone(), &documents, &dir);
+        documents.add_observer(plugin_diagnostics.clone());
         let project = Arc::new(Project {
+            plugin_diagnostics,
             trusted: Arc::new(AtomicBool::new(false)),
             sink,
             languages,
diff --git a/crates/ide-host/tests/plugin_diagnostics.rs b/crates/ide-host/tests/plugin_diagnostics.rs
new file mode 100644
index 000000000..379296785
--- /dev/null
+++ b/crates/ide-host/tests/plugin_diagnostics.rs
@@ -0,0 +1,354 @@
+//! Real Wasm provider dispatch and the document-edit path used locally and over RPC.
+use ide_core::{CancellationToken, ChangeSet, Diagnostic, IdeEvent, Pos, Range, TextChange};
+use ide_host::plugins::{Consent, HostWorkspace, PluginHost, set_editor_providers};
+use ide_host::{Host, HostConfig, ops};
+use ide_plugin::{Invocation, Limits, ProviderDocument};
+use parking_lot::Mutex;
+use std::path::{Path, PathBuf};
+use std::sync::Arc;
+use std::time::{Duration, Instant};
+
+const ID: &str = "test.diagnostics";
+const SOURCE: &str = "plugin-provider:test.diagnostics";
+
+fn fixture() -> PathBuf {
+    Path::new(env!("CARGO_MANIFEST_DIR")).join("../ide-plugin/tests/fixtures/diagnostics")
+}
+
+fn plugins(dir: &Path, limits: Limits) -> Arc<PluginHost> {
+    let host = Arc::new(PluginHost::new(dir.join("plugins"), Arc::new(|_: Option<&str>, _| {}), limits).unwrap());
+    host.install_from_dir(&fixture(), &Consent::all()).unwrap();
+    host
+}
+
+fn generous() -> Limits {
+    Limits { edit_soft: Duration::from_secs(5), edit_hard: Duration::from_secs(10), ..Limits::default() }
+}
+
+fn doc(root: &Path, language: &str, text: &str) -> ProviderDocument {
+    ProviderDocument { path: root.join("a.txt"), language: language.into(), version: 42, text: text.into() }
+}
+
+#[test]
+fn declared_languages_receive_versioned_text_and_utf16_ranges() {
+    let tmp = tempfile::tempdir().unwrap();
+    let host = plugins(tmp.path(), generous());
+    let result = host.provide_diagnostics(&doc(tmp.path(), "text", "😀BAD\nBAD"), &CancellationToken::new());
+    assert_eq!(result.len(), 1);
+    assert_eq!(result[0].0, ID);
+    let items = &result[0].1;
+    assert_eq!(items.len(), 2);
+    assert_eq!(items[0].range, Range::new(Pos::new(0, 2), Pos::new(0, 5)));
+    assert_eq!(items[1].range, Range::new(Pos::new(1, 0), Pos::new(1, 3)));
+    assert_eq!(items[0].message, "BAD in text at version 42");
+    assert_eq!(items[0].code.as_deref(), Some("bad-word"));
+    assert_eq!(items[0].server.as_deref(), Some(ID));
+    assert!(host.provide_diagnostics(&doc(tmp.path(), "rust", "BAD"), &CancellationToken::new()).is_empty());
+}
+
+#[test]
+fn provider_diagnostics_have_the_same_bounds_and_tags_as_manual_publish() {
+    let tmp = tempfile::tempdir().unwrap();
+    let host = plugins(tmp.path(), generous());
+    let result = host.provide_diagnostics(&doc(tmp.path(), "text", "limits"), &CancellationToken::new());
+    let items = &result[0].1;
+    assert_eq!(items.len(), 5000);
+    assert_eq!(items[0].message.len(), 4096);
+    assert_eq!(items[0].source.as_ref().unwrap().len(), 128);
+    assert_eq!(items[0].code.as_ref().unwrap().len(), 128);
+    assert!(items[0].unnecessary && items[0].deprecated);
+}
+
+#[test]
+fn the_export_does_not_need_project_read_permission() {
+    let tmp = tempfile::tempdir().unwrap();
+    let package = tmp.path().join("no-capability");
+    std::fs::create_dir_all(package.join("dist")).unwrap();
+    std::fs::copy(fixture().join("dist/plugin.wasm"), package.join("dist/plugin.wasm")).unwrap();
+    let manifest = std::fs::read_to_string(fixture().join("plugin.toml")).unwrap();
+    std::fs::write(package.join("plugin.toml"), manifest.replace("[capabilities]\nrequired = [\"project.read\"]", ""))
+        .unwrap();
+    let host = PluginHost::new(tmp.path().join("plugins"), Arc::new(|_: Option<&str>, _| {}), generous()).unwrap();
+    host.install_from_dir(&package, &Consent::default()).unwrap();
+    assert_eq!(host.provide_diagnostics(&doc(tmp.path(), "text", "BAD"), &CancellationToken::new()).len(), 1);
+    assert!(host.run_command(ID, "publish", Some("/project/a.txt"), Invocation::default()).is_err());
+}
+
+#[test]
+fn diagnostics_is_an_api_1_3_addition() {
+    let tmp = tempfile::tempdir().unwrap();
+    let package = tmp.path().join("old");
+    std::fs::create_dir_all(package.join("dist")).unwrap();
+    std::fs::copy(fixture().join("dist/plugin.wasm"), package.join("dist/plugin.wasm")).unwrap();
+    let manifest = std::fs::read_to_string(fixture().join("plugin.toml")).unwrap();
+    std::fs::write(package.join("plugin.toml"), manifest.replace("^1.3", "^1.0")).unwrap();
+    let host = PluginHost::new(tmp.path().join("plugins"), Arc::new(|_: Option<&str>, _| {}), generous()).unwrap();
+    assert!(host.install_from_dir(&package, &Consent::all()).unwrap_err().message.contains("new in plugin API 1.3"));
+}
+
+#[test]
+fn late_and_cancelled_answers_are_dropped_without_disabling_the_plugin() {
+    let tmp = tempfile::tempdir().unwrap();
+    let host = plugins(tmp.path(), Limits { edit_soft: Duration::from_millis(10), ..generous() });
+    assert!(host.provide_diagnostics(&doc(tmp.path(), "text", "slow BAD"), &CancellationToken::new()).is_empty());
+    let cancel = CancellationToken::new();
+    cancel.cancel();
+    assert!(host.provide_diagnostics(&doc(tmp.path(), "text", "BAD"), &cancel).is_empty());
+    assert_eq!(host.run_command(ID, "calls", None, Invocation::default()).unwrap().as_deref(), Some("1"));
+}
+
+#[test]
+fn cancelling_a_queued_provider_does_not_interrupt_another_windows_command() {
+    let tmp = tempfile::tempdir().unwrap();
+    let host = plugins(tmp.path(), generous());
+    host.run_command(ID, "calls", None, Invocation::default()).unwrap();
+    let waiter = {
+        let host = host.clone();
+        std::thread::spawn(move || host.run_command(ID, "wait", None, Invocation::default()))
+    };
+    std::thread::sleep(Duration::from_millis(50));
+    let cancel = CancellationToken::new();
+    let canceller = {
+        let cancel = cancel.clone();
+        std::thread::spawn(move || {
+            std::thread::sleep(Duration::from_millis(30));
+            cancel.cancel();
+        })
+    };
+    assert!(host.provide_diagnostics(&doc(tmp.path(), "text", "BAD"), &cancel).is_empty());
+    canceller.join().unwrap();
+    assert_eq!(waiter.join().unwrap().unwrap().as_deref(), Some("finished"));
+    assert_eq!(host.run_command(ID, "calls", None, Invocation::default()).unwrap().as_deref(), Some("0"));
+}
+
+#[test]
+fn editor_requests_expire_in_the_queue_without_running_after_a_command() {
+    let tmp = tempfile::tempdir().unwrap();
+    let host = plugins(tmp.path(), Limits { edit_soft: Duration::from_millis(10), ..generous() });
+    host.run_command(ID, "calls", None, Invocation::default()).unwrap();
+    let waiter = {
+        let host = host.clone();
+        std::thread::spawn(move || host.run_command(ID, "wait", None, Invocation::default()))
+    };
+    std::thread::sleep(Duration::from_millis(50));
+    assert!(host.provide_diagnostics(&doc(tmp.path(), "text", "BAD"), &CancellationToken::new()).is_empty());
+    assert_eq!(waiter.join().unwrap().unwrap().as_deref(), Some("finished"));
+    assert_eq!(host.run_command(ID, "calls", None, Invocation::default()).unwrap().as_deref(), Some("0"));
+    assert_eq!(host.info_of(ID).unwrap().stats.slow_calls, 1);
+}
+
+#[test]
+fn typing_on_cancels_a_running_provider_before_its_hard_deadline() {
+    let tmp = tempfile::tempdir().unwrap();
+    let host = plugins(tmp.path(), Limits { fuel: u64::MAX, ..generous() });
+    host.run_command(ID, "calls", None, Invocation::default()).unwrap();
+    let cancel = CancellationToken::new();
+    let canceller = {
+        let cancel = cancel.clone();
+        std::thread::spawn(move || {
+            std::thread::sleep(Duration::from_millis(30));
+            cancel.cancel();
+        })
+    };
+    let started = Instant::now();
+    assert!(host.provide_diagnostics(&doc(tmp.path(), "text", "spin BAD"), &cancel).is_empty());
+    assert!(started.elapsed() < Duration::from_secs(2));
+    canceller.join().unwrap();
+}
+
+// This executable has one edit-path test because editor providers are installed once per process.
+type Events = Arc<Mutex<Vec<(String, IdeEvent)>>>;
+
+fn runtime_host(base: &Path, events: Events) -> Arc<Host> {
+    Arc::new(Host::new(HostConfig {
+        config_dir: base.join("config"),
+        data_dir: base.join("data"),
+        local_data_dir: base.join("data"),
+        languages: Arc::new(ide_language::LanguageRegistry::load(None).unwrap()),
+        syntax: Arc::default(),
+        sink_for: Box::new(move |window| {
+            let (events, window) = (events.clone(), window.to_owned());
+            Arc::new(move |event: IdeEvent| events.lock().push((window.clone(), event)))
+        }),
+        owner: |w| w,
+        runtime: tokio::runtime::Handle::current(),
+        project_environment: false,
+    }))
+}
+
+fn latest(events: &Events, window: &str, source: &str) -> Option<Vec<Diagnostic>> {
+    events.lock().iter().rev().find_map(|(w, e)| match e {
+        IdeEvent::Diagnostics { source: s, items, .. } if w == window && s == source => Some(items.clone()),
+        _ => None,
+    })
+}
+
+async fn wait_for(events: &Events, window: &str, predicate: impl Fn(&[Diagnostic]) -> bool) {
+    wait_for_source(events, window, SOURCE, predicate).await;
+}
+
+async fn wait_for_source(events: &Events, window: &str, source: &str, predicate: impl Fn(&[Diagnostic]) -> bool) {
+    let start = Instant::now();
+    loop {
+        if latest(events, window, source).is_some_and(|items| predicate(&items)) {
+            return;
+        }
+        assert!(start.elapsed() < Duration::from_secs(5), "missing diagnostics for {window}");
+        tokio::time::sleep(Duration::from_millis(10)).await;
+    }
+}
+
+fn replace(host: &Host, window: &str, info: &ide_workspace::DocumentInfo, text: &str) -> u32 {
+    let project = host.project(window).unwrap();
+    let snapshot = project.documents.snapshot(info.id).unwrap();
+    let len = snapshot.text.encode_utf16().count() as u32;
+    ops::doc::edit(
+        host,
+        window,
+        info.id,
+        snapshot.version,
+        ChangeSet { changes: vec![TextChange { from: 0, to: len, insert: text.into() }] },
+    )
+    .unwrap()
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 4)]
+async fn typing_is_debounced_versioned_and_scoped_to_document_project_and_window_lifetimes() {
+    let tmp = tempfile::tempdir().unwrap();
+    let root = dunce::canonicalize(tmp.path()).unwrap();
+    let path = root.join("a.txt");
+    std::fs::write(&path, "clean").unwrap();
+    let events: Events = Arc::default();
+    let host = runtime_host(&root.join("app"), events.clone());
+    let plugins = plugins(&root, generous());
+    plugins.set_workspace(Some(Arc::new(HostWorkspace(Arc::downgrade(&host)))));
+    set_editor_providers(Some(&plugins));
+    let left = host.open_light("left", &path).unwrap();
+    host.open_light("right", &path).unwrap();
+    let a = ops::doc::open(&host, "left", path.clone()).await.unwrap();
+    let b = ops::doc::open(&host, "right", path.clone()).await.unwrap();
+    let second_tab = ops::doc::open(&host, "right", path.clone()).await.unwrap();
+    assert_eq!(b.id, second_tab.id);
+    wait_for(&events, "left", |items| items.is_empty()).await;
+    wait_for(&events, "right", |items| items.is_empty()).await;
+
+    let calls: u64 = plugins.run_command(ID, "calls", None, Invocation::default()).unwrap().unwrap().parse().unwrap();
+    events.lock().clear();
+    replace(&host, "left", &a, "BAD");
+    tokio::time::sleep(Duration::from_millis(100)).await;
+    let version = replace(&host, "left", &a, "😀BAD");
+    tokio::time::sleep(Duration::from_millis(150)).await;
+    assert!(latest(&events, "left", SOURCE).is_none(), "300ms after the latest edit");
+    wait_for(&events, "left", |items| !items.is_empty()).await;
+    assert_eq!(
+        latest(&events, "left", SOURCE).unwrap()[0].message,
+        format!("BAD in {} at version {version}", a.language)
+    );
+    assert!(latest(&events, "right", SOURCE).is_none(), "other window has its own buffer");
+    assert_eq!(std::fs::read_to_string(&path).unwrap(), "clean", "no save required");
+    let after: u64 = plugins.run_command(ID, "calls", None, Invocation::default()).unwrap().unwrap().parse().unwrap();
+    assert_eq!(after, calls + 1, "the edit burst was coalesced");
+
+    plugins.run_command(ID, "publish", path.to_str(), Invocation::default()).unwrap();
+    let manual_window = events.lock().iter().find_map(|(window, event)| matches!(event, IdeEvent::Diagnostics { source, items, .. } if source == "plugin:test.diagnostics" && !items.is_empty()).then(|| window.clone())).unwrap();
+    assert_eq!(latest(&events, &manual_window, "plugin:test.diagnostics").unwrap()[0].message, "Manual problem");
+    replace(&host, "left", &a, "clean again");
+    wait_for(&events, "left", |items| items.is_empty()).await;
+    assert_eq!(latest(&events, &manual_window, "plugin:test.diagnostics").unwrap()[0].message, "Manual problem");
+
+    events.lock().clear();
+    replace(&host, "left", &a, "slow BAD");
+    tokio::time::sleep(Duration::from_millis(350)).await;
+    replace(&host, "left", &a, "latest clean");
+    wait_for(&events, "left", |items| items.is_empty()).await;
+    assert!(
+        !events.lock().iter().any(|(_, e)| matches!(e, IdeEvent::Diagnostics { items, .. } if !items.is_empty())),
+        "superseded in-flight answers never publish"
+    );
+
+    replace(&host, "right", &b, "BAD right");
+    wait_for(&events, "right", |items| !items.is_empty()).await;
+    ops::doc::close(&host, "right", b.id).unwrap();
+    assert!(!latest(&events, "right", SOURCE).unwrap().is_empty(), "another pane still owns this document");
+    ops::doc::close(&host, "right", second_tab.id).unwrap();
+    wait_for(&events, "right", |items| items.is_empty()).await;
+    replace(&host, "left", &a, "BAD left");
+    wait_for(&events, "left", |items| !items.is_empty()).await;
+    plugins.set_enabled(ID, false).unwrap();
+    wait_for(&events, "left", |items| items.is_empty()).await;
+    plugins.set_enabled(ID, true).unwrap();
+
+    events.lock().clear();
+    replace(&host, "left", &a, "slow BAD closing");
+    tokio::time::sleep(Duration::from_millis(350)).await;
+    host.close_project("left");
+    // Keep the old Project alive deliberately: window reuse must still cancel it.
+    assert_eq!(left.documents.snapshot(a.id).unwrap().text, "slow BAD closing");
+    host.open_light("left", &path).unwrap();
+    let reopened = ops::doc::open(&host, "left", path.clone()).await.unwrap();
+    wait_for(&events, "left", |items| items.is_empty()).await;
+    assert!(!events.lock().iter().any(|(_, e)| matches!(e, IdeEvent::Diagnostics { items, .. } if !items.is_empty())));
+    // Project plugins receive only snapshots from the project that owns their declaration.
+    let project_package = root.join(ide_host::plugins::DEV_PLUGINS_DIR).join("diagnostics");
+    std::fs::create_dir_all(project_package.join("dist")).unwrap();
+    std::fs::copy(fixture().join("dist/plugin.wasm"), project_package.join("dist/plugin.wasm")).unwrap();
+    let manifest = std::fs::read_to_string(fixture().join("plugin.toml")).unwrap();
+    std::fs::write(project_package.join("plugin.toml"), manifest.replace(ID, "project.diagnostics")).unwrap();
+    plugins.set_project_policy(Arc::new(|_| true));
+    plugins.sync_project(&root);
+    plugins.grant("project.diagnostics", &Consent::all()).unwrap();
+    replace(&host, "left", &reopened, "BAD in project");
+    wait_for(&events, "left", |items| !items.is_empty()).await;
+    let project_source = "plugin-provider:project.diagnostics";
+    wait_for_source(&events, "left", project_source, |items| !items.is_empty()).await;
+    let elsewhere = root.join("other");
+    std::fs::create_dir_all(&elsewhere).unwrap();
+    let other_path = elsewhere.join("other.txt");
+    std::fs::write(&other_path, "BAD outside").unwrap();
+    host.open_light("elsewhere", &other_path).unwrap();
+    ops::doc::open(&host, "elsewhere", other_path).await.unwrap();
+    wait_for(&events, "elsewhere", |items| !items.is_empty()).await;
+    assert!(latest(&events, "elsewhere", project_source).is_none());
+    plugins.restrict_project(&root);
+    assert!(latest(&events, "left", project_source).unwrap().is_empty());
+    // A completed answer may still be waiting for a sibling when its plugin crashes.
+    let sibling = root.join("slow-sibling");
+    std::fs::create_dir_all(sibling.join("dist")).unwrap();
+    std::fs::copy(fixture().join("dist/plugin.wasm"), sibling.join("dist/plugin.wasm")).unwrap();
+    let manifest = std::fs::read_to_string(fixture().join("plugin.toml")).unwrap();
+    std::fs::write(
+        sibling.join("plugin.toml"),
+        manifest.replace(ID, "test.slow").replace("[\"text\", \"plaintext\"]", "[\"plaintext\"]"),
+    )
+    .unwrap();
+    plugins.install_from_dir(&sibling, &Consent::all()).unwrap();
+    plugins.run_command("test.slow", "calls", None, Invocation::default()).unwrap();
+    let calls = plugins.run_command(ID, "calls", None, Invocation::default()).unwrap();
+    events.lock().clear();
+    replace(&host, "left", &reopened, "BAD completed before crash");
+    tokio::time::sleep(Duration::from_millis(200)).await;
+    let waiter = {
+        let plugins = plugins.clone();
+        std::thread::spawn(move || plugins.run_command("test.slow", "wait", None, Invocation::default()))
+    };
+    let started = Instant::now();
+    while plugins.run_command(ID, "calls", None, Invocation::default()).unwrap() == calls {
+        assert!(started.elapsed() < Duration::from_secs(5));
+        tokio::time::sleep(Duration::from_millis(5)).await;
+    }
+    assert!(
+        latest(&events, "left", SOURCE).is_none_or(|items| items.is_empty()),
+        "the sibling still holds the result: {:?}",
+        latest(&events, "left", SOURCE)
+    );
+    assert!(plugins.provide_diagnostics(&doc(&root, "text", "panic"), &CancellationToken::new()).is_empty());
+    waiter.join().unwrap().unwrap();
+    wait_for_source(&events, "left", "plugin-provider:test.slow", |items| !items.is_empty()).await;
+    assert!(
+        latest(&events, "left", SOURCE).is_none_or(|items| items.is_empty()),
+        "a crash invalidates completed answers"
+    );
+    ops::doc::close(&host, "left", reopened.id).unwrap();
+    host.shutdown().await;
+    set_editor_providers(None);
+}
diff --git a/crates/ide-plugin/src/actor.rs b/crates/ide-plugin/src/actor.rs
index e95a7e0bb..fc678f125 100644
--- a/crates/ide-plugin/src/actor.rs
+++ b/crates/ide-plugin/src/actor.rs
@@ -13,6 +13,7 @@
 //! idle reclaim ends it.
 
 use crate::runtime::{CallCancel, CallError, Runtime};
+use std::panic::{AssertUnwindSafe, catch_unwind};
 use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
 use std::sync::{Arc, Mutex, mpsc};
 use std::thread::JoinHandle;
@@ -20,6 +21,17 @@ use std::time::{Duration, Instant};
 
 type Job = Box<dyn FnOnce(&mut Option<Runtime>) + Send>;
 
+fn catch_call<R>(f: impl FnOnce() -> Result<R, CallError>) -> Result<R, CallError> {
+    catch_unwind(AssertUnwindSafe(f)).unwrap_or_else(|panic| {
+        let message = panic
+            .downcast_ref::<String>()
+            .map(String::as_str)
+            .or_else(|| panic.downcast_ref::<&str>().copied())
+            .unwrap_or("unknown panic");
+        Err(CallError::Trap(format!("plugin actor panicked: {message}")))
+    })
+}
+
 /// Why an [`Actor::call`] produced no result.
 #[derive(Debug)]
 pub enum ActorError {
@@ -85,15 +97,24 @@ impl Actor {
         let cancel = runtime.cancel_handle();
         let alive = Arc::new(AtomicBool::new(true));
         let busy = Arc::new(AtomicBool::new(false));
+        let crash = Arc::new(Mutex::new(None));
         let last_used = Arc::new(AtomicU64::new(0));
         let epoch = Instant::now();
         let thread = {
-            let (alive, busy, last_used) = (alive.clone(), busy.clone(), last_used.clone());
+            let (alive, busy, last_used, crash) = (alive.clone(), busy.clone(), last_used.clone(), crash.clone());
             std::thread::Builder::new().name(format!("plugin:{name}")).spawn(move || {
                 let mut slot = Some(runtime);
                 while let Ok(job) = rx.recv() {
                     busy.store(true, Ordering::Release);
-                    job(&mut slot);
+                    // A completion callback may panic too; never leave a dead thread marked alive.
+                    if let Err(CallError::Trap(error)) = catch_call(|| {
+                        job(&mut slot);
+                        Ok(())
+                    }) {
+                        *crash.lock().unwrap_or_else(|e| e.into_inner()) = Some(error);
+                        alive.store(false, Ordering::Release);
+                        slot = None;
+                    }
                     last_used.store(epoch.elapsed().as_millis() as u64, Ordering::Release);
                     busy.store(false, Ordering::Release);
                     if slot.is_none() {
@@ -113,7 +134,7 @@ impl Actor {
             thread: Mutex::new(Some(thread)),
             cancel,
             alive,
-            crash: Arc::default(),
+            crash,
             busy,
             last_used,
             epoch,
@@ -148,7 +169,7 @@ impl Actor {
                 return;
             }
             let Some(rt) = slot.as_mut() else { return };
-            let outcome = f(rt);
+            let outcome = catch_call(|| f(rt));
             if let Err(CallError::Trap(e)) = &outcome {
                 *crash.lock().unwrap_or_else(|e| e.into_inner()) = Some(e.clone());
                 // Before the reply: the caller sees the actor dead.
@@ -174,21 +195,59 @@ impl Actor {
         cancel: &ide_core::CancellationToken,
         grace: Duration,
         f: impl FnOnce(&mut Runtime) -> Result<R, CallError> + Send + 'static,
+    ) -> Result<R, ActorError> {
+        self.call_cancellable_before(cancel, grace, None, f)
+    }
+
+    /// A cancellable editor call: queued work expires after `soft`, and a
+    /// successful answer produced later is dropped. Running work still has
+    /// its runtime hard deadline and can be cancelled by further typing.
+    pub fn call_edit_cancellable<R: Send + 'static>(
+        &self,
+        cancel: &ide_core::CancellationToken,
+        grace: Duration,
+        soft: Duration,
+        f: impl FnOnce(&mut Runtime) -> Result<R, CallError> + Send + 'static,
+    ) -> Result<R, ActorError> {
+        self.call_cancellable_before(cancel, grace, Some(Instant::now() + soft), f)
+    }
+
+    fn call_cancellable_before<R: Send + 'static>(
+        &self,
+        cancel: &ide_core::CancellationToken,
+        grace: Duration,
+        deadline: Option<Instant>,
+        f: impl FnOnce(&mut Runtime) -> Result<R, CallError> + Send + 'static,
     ) -> Result<R, ActorError> {
         let (reply, result) = mpsc::sync_channel(1);
         let (crash, alive) = (self.crash.clone(), self.alive.clone());
         let skip = cancel.clone();
+        let running = Arc::new(Mutex::new(false));
+        let in_job = running.clone();
         let job: Job = Box::new(move |slot| {
-            if skip.is_cancelled() {
-                return;
-            }
             let Some(rt) = slot.as_mut() else { return };
-            let outcome = f(rt);
+            {
+                let mut running = in_job.lock().unwrap_or_else(|e| e.into_inner());
+                if skip.is_cancelled() {
+                    return;
+                }
+                if deadline.is_some_and(|t| Instant::now() >= t) {
+                    let _ = reply.send(Err(ActorError::SoftTimeout));
+                    return;
+                }
+                *running = true;
+            }
+            let outcome = catch_call(|| f(rt));
+            *in_job.lock().unwrap_or_else(|e| e.into_inner()) = false;
             if let Err(CallError::Trap(e)) = &outcome {
                 *crash.lock().unwrap_or_else(|e| e.into_inner()) = Some(e.clone());
                 alive.store(false, Ordering::Release);
                 *slot = None;
             }
+            let outcome = match outcome {
+                Ok(_) if deadline.is_some_and(|t| Instant::now() > t) => Err(ActorError::SoftTimeout),
+                other => other.map_err(ActorError::Call),
+            };
             let _ = reply.send(outcome);
         });
         {
@@ -203,25 +262,34 @@ impl Actor {
                     drop(outcome);
                     return Err(ActorError::Cancelled);
                 }
-                Ok(outcome) => return outcome.map_err(ActorError::Call),
+                Ok(outcome) => return outcome,
                 Err(mpsc::RecvTimeoutError::Disconnected) => {
                     return Err(if cancel.is_cancelled() { ActorError::Cancelled } else { ActorError::Stopped });
                 }
                 Err(mpsc::RecvTimeoutError::Timeout) => {}
             }
             if !cancel.is_cancelled() {
+                if deadline.is_some_and(|t| Instant::now() >= t) && !*running.lock().unwrap_or_else(|e| e.into_inner())
+                {
+                    return Err(ActorError::SoftTimeout);
+                }
                 continue;
             }
             match cancelled_at {
                 None => {
                     cancelled_at = Some(Instant::now());
-                    if self.is_busy() {
-                        self.cancel.cancel_soft();
+                    let running = running.lock().unwrap_or_else(|e| e.into_inner());
+                    if !*running {
+                        return Err(ActorError::Cancelled);
                     }
+                    self.cancel.cancel_soft();
                 }
                 Some(at) if at.elapsed() >= grace => {
                     // Did not return in time: interrupt it (the instance is rebuilt).
-                    self.cancel();
+                    let running = running.lock().unwrap_or_else(|e| e.into_inner());
+                    if *running {
+                        self.cancel();
+                    }
                     return Err(ActorError::Cancelled);
                 }
                 Some(_) => {}
@@ -239,7 +307,7 @@ impl Actor {
         let (crash, alive) = (self.crash.clone(), self.alive.clone());
         let job: Job = Box::new(move |slot| {
             let Some(rt) = slot.as_mut() else { return done(Err(ActorError::Stopped)) };
-            let outcome = f(rt);
+            let outcome = catch_call(|| f(rt));
             if let Err(CallError::Trap(e)) = &outcome {
                 *crash.lock().unwrap_or_else(|e| e.into_inner()) = Some(e.clone());
                 alive.store(false, Ordering::Release);
diff --git a/crates/ide-plugin/src/runtime.rs b/crates/ide-plugin/src/runtime.rs
index 8c075a7c8..763913116 100644
--- a/crates/ide-plugin/src/runtime.rs
+++ b/crates/ide-plugin/src/runtime.rs
@@ -632,6 +632,7 @@ struct Exports {
     views: Option<wit_view::Guest>,
     semantic: Option<wit_sem::Guest>,
     details: Option<wit_detail::Guest>,
+    diagnostics: Option<crate::wit_host::diagnostics_bindings::exports::openidea::plugin::diagnostics_provider::Guest>,
     hover: Option<wit_hover::Guest>,
     commit_checks: Option<wit_cc::Guest>,
     inlay: Option<wit_inlay::Guest>,
@@ -719,6 +720,8 @@ impl Runtime {
         let view_indices = wit_view::GuestIndices::new(&pre).ok();
         let semantic_indices = wit_sem::GuestIndices::new(&pre).ok();
         let detail_indices = wit_detail::GuestIndices::new(&pre).ok();
+        use crate::wit_host::diagnostics_bindings::exports::openidea::plugin::diagnostics_provider as wit_diag;
+        let diagnostics_indices = wit_diag::GuestIndices::new(&pre).ok();
         let hover_indices = wit_hover::GuestIndices::new(&pre).ok();
         let commit_check_indices = wit_cc::GuestIndices::new(&pre).ok();
         let inlay_indices = wit_inlay::GuestIndices::new(&pre).ok();
@@ -753,6 +756,10 @@ impl Runtime {
             Some(indices) => Some(indices.load(&mut store, &instance).map_err(api_hint)?),
             None => None,
         };
+        let diagnostics = match diagnostics_indices {
+            Some(i) => Some(i.load(&mut store, &instance).map_err(api_hint)?),
+            None => None,
+        };
         let hover = match hover_indices {
             Some(indices) => Some(indices.load(&mut store, &instance).map_err(api_hint)?),
             None => None,
@@ -779,6 +786,7 @@ impl Runtime {
                 indexer,
                 semantic,
                 details,
+                diagnostics,
                 hover,
                 commit_checks,
                 inlay,
@@ -1075,6 +1083,27 @@ impl Runtime {
             .collect())
     }
 
+    pub fn provide_diagnostics(
+        &mut self,
+        doc: &ProviderDocument,
+        timeout: Duration,
+    ) -> Result<Vec<ide_core::Diagnostic>, CallError> {
+        use crate::wit_host::diagnostics_bindings::exports::openidea::plugin::diagnostics_provider as w;
+        if self.exports.diagnostics.is_none() {
+            return Err(CallError::missing_export("diagnostics-provider"));
+        }
+        let d = w::Document {
+            path: to_ipc(&doc.path),
+            language: doc.language.clone(),
+            version: doc.version,
+            text: doc.text.clone(),
+        };
+        let items = self.call(Invocation::default(), timeout, |e, store| {
+            e.diagnostics.as_ref().expect("checked").call_diagnostics(store, &d)
+        })?;
+        Ok(crate::wit_host::diagnostics_from_wit(items, &self.store.data().plugin_id))
+    }
+
     pub fn provide_hover(
         &mut self,
         doc: &ProviderDocument,
diff --git a/crates/ide-plugin/src/wit_host.rs b/crates/ide-plugin/src/wit_host.rs
index a0f080273..10370a481 100644
--- a/crates/ide-plugin/src/wit_host.rs
+++ b/crates/ide-plugin/src/wit_host.rs
@@ -922,26 +922,7 @@ impl diagnostics::Host for StoreData {
         if let Err(e) = self.require(Capability::ProjectRead) {
             return Ok(Err(e));
         }
-        let source = self.plugin_id.clone();
-        let items = items
-            .into_iter()
-            .take(MAX_DIAGNOSTICS)
-            .map(|d| ide_core::Diagnostic {
-                range: ide_core::Range::new(pos(d.range.start), pos(d.range.end)),
-                severity: match d.severity {
-                    diagnostics::Severity::Error => ide_core::Severity::Error,
-                    diagnostics::Severity::Warning => ide_core::Severity::Warning,
-                    diagnostics::Severity::Info => ide_core::Severity::Info,
-                    diagnostics::Severity::Hint => ide_core::Severity::Hint,
-                },
-                message: clip(d.message, 4096),
-                source: Some(d.source.map_or_else(|| source.clone(), |s| clip(s, 128))),
-                code: d.code.map(|c| clip(c, 128)),
-                unnecessary: d.tags.iter().any(|t| t == "unnecessary"),
-                deprecated: d.tags.iter().any(|t| t == "deprecated"),
-                server: Some(source.clone()),
-            })
-            .collect();
+        let items = diagnostics_from_wit(items, &self.plugin_id);
         Ok(self.host.publish_diagnostics(Path::new(&path), items).map_err(to_wit))
     }
 }
@@ -1397,3 +1378,35 @@ mod project_ui_tests {
         assert!(validate_ui_path(&format!("/{}", "x".repeat(8192))).is_err());
     }
 }
+
+pub(crate) mod diagnostics_bindings {
+    wasmtime::component::bindgen!({
+        world: "editor-diagnostics", path: "../../wit",
+        with: {
+            "openidea:plugin/types": super::bindings::openidea::plugin::types,
+            "openidea:plugin/diagnostics": super::bindings::openidea::plugin::diagnostics,
+        },
+    });
+}
+
+pub(crate) fn diagnostics_from_wit(items: Vec<diagnostics::Diagnostic>, source: &str) -> Vec<ide_core::Diagnostic> {
+    items
+        .into_iter()
+        .take(MAX_DIAGNOSTICS)
+        .map(|d| ide_core::Diagnostic {
+            range: ide_core::Range::new(pos(d.range.start), pos(d.range.end)),
+            severity: match d.severity {
+                diagnostics::Severity::Error => ide_core::Severity::Error,
+                diagnostics::Severity::Warning => ide_core::Severity::Warning,
+                diagnostics::Severity::Info => ide_core::Severity::Info,
+                diagnostics::Severity::Hint => ide_core::Severity::Hint,
+            },
+            message: clip(d.message, 4096),
+            source: Some(d.source.map_or_else(|| source.to_owned(), |s| clip(s, 128))),
+            code: d.code.map(|c| clip(c, 128)),
+            unnecessary: d.tags.iter().any(|t| t == "unnecessary"),
+            deprecated: d.tags.iter().any(|t| t == "deprecated"),
+            server: Some(source.to_owned()),
+        })
+        .collect()
+}
diff --git a/crates/ide-plugin/tests/api_compat.rs b/crates/ide-plugin/tests/api_compat.rs
index 9f27c96a1..7926dae3f 100644
--- a/crates/ide-plugin/tests/api_compat.rs
+++ b/crates/ide-plugin/tests/api_compat.rs
@@ -30,6 +30,7 @@ fn components() -> Vec<PathBuf> {
         repo().join("crates/ide-plugin/tests/fixtures/indexer/dist/plugin.wasm"),
         repo().join("crates/ide-plugin/tests/fixtures/semantic-tokens/dist/plugin.wasm"),
         repo().join("crates/ide-plugin/tests/fixtures/hover/dist/plugin.wasm"),
+        repo().join("crates/ide-plugin/tests/fixtures/diagnostics/dist/plugin.wasm"),
         repo().join("crates/ide-plugin/tests/fixtures/inlay-hints/dist/plugin.wasm"),
         repo().join("crates/ide-plugin/tests/fixtures/symbols/dist/plugin.wasm"),
     ];
diff --git a/crates/ide-plugin/tests/fixtures/commit/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/commit/dist/plugin.wasm
index 5b8ede3d6..bc98cc38d 100644
Binary files a/crates/ide-plugin/tests/fixtures/commit/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/commit/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/commit/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/commit/dist/plugin.wasm.sources
index 6ec88cb35..635baa55c 100644
--- a/crates/ide-plugin/tests/fixtures/commit/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/commit/dist/plugin.wasm.sources
@@ -1 +1 @@
-2652fb97735511f78576d5a16f685871bd7ab12df94795f14984bc819fe0b593
+24726dac5ce264f5d451956def099e0002ec721e4828bc7852ad1dcabcb4bcba
diff --git a/crates/ide-plugin/tests/fixtures/detail-views/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/detail-views/dist/plugin.wasm
index 20743313d..cab230a16 100644
Binary files a/crates/ide-plugin/tests/fixtures/detail-views/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/detail-views/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/detail-views/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/detail-views/dist/plugin.wasm.sources
index dc9bf4212..81b1b8dba 100644
--- a/crates/ide-plugin/tests/fixtures/detail-views/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/detail-views/dist/plugin.wasm.sources
@@ -1 +1 @@
-41cf712d387210fea3e102f3f590b05c69b56814b742504a40c53f160874e926
+833c378fabd0c3ec71e5c372e51049cb4fcd8d58e4992199eaf6090b3c1235d8
diff --git a/crates/ide-plugin/tests/fixtures/diagnostics/Cargo.lock b/crates/ide-plugin/tests/fixtures/diagnostics/Cargo.lock
new file mode 100644
index 000000000..0e18d38a4
--- /dev/null
+++ b/crates/ide-plugin/tests/fixtures/diagnostics/Cargo.lock
@@ -0,0 +1,333 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "anyhow"
+version = "1.0.104"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "330a5ed07fa54e4702c9d6c4174f74427fc0ef6e214bbd677ae50a5099946470"
+
+[[package]]
+name = "bitflags"
+version = "2.13.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3ded4057c258ba199e2d26386d3af3780957ecaee6c4ef4041c6b4b8b97c0b06"
+
+[[package]]
+name = "equivalent"
+version = "1.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "00d174d5400e5e8fd687ad1049e2f578285fa914201b1af7e8b112a4546bd826"
+
+[[package]]
+name = "foldhash"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "77ce24cb58228fbb8aa041425bb1050850ac19177686ea6e0f41a70416f56fdb"
+
+[[package]]
+name = "hashbrown"
+version = "0.17.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ed5909b6e89a2db4456e54cd5f673791d7eca6732202bbf2a9cc504fe2f9b84a"
+dependencies = [
+ "foldhash",
+]
+
+[[package]]
+name = "heck"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2304e00983f87ffb38b55b444b5e3b60a884b5d30c0fca7d82fe33449bbe55ea"
+
+[[package]]
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+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cc4e190f5d26ca7051642629da2c52fc03bde85a03197c99408dcd291734c855"
+dependencies = [
+ "equivalent",
+ "hashbrown",
+ "serde",
+ "serde_core",
+]
+
+[[package]]
+name = "itoa"
+version = "1.0.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8f42a60cbdf9a97f5d2305f08a87dc4e09308d1276d28c869c684d7777685682"
+
+[[package]]
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+checksum = "09edd9e8b54e49e587e4f6295a7d29c3ea94d469cb40ab8ca70b288248a81db2"
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5d15f86d12da44cd8d4ec3c73984537eb7f4cadcb9776a575a0a8a05ca11005c"
+
+[[package]]
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+version = "0.3.0"
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+checksum = "6e7b3a5bbb2f63aaa223a671ea1bd0e7bc16bd30ce387324cf63995deaddbbd2"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
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+version = "2.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf8baf1c55e62ffcace7a9f06f4bd9cd3f0c4beb022d3b367256b91b87513d98"
+
+[[package]]
+name = "openidea-plugin"
+version = "0.1.0"
+dependencies = [
+ "wit-bindgen",
+]
+
+[[package]]
+name = "openidea-test-diagnostics"
+version = "0.1.0"
+dependencies = [
+ "openidea-plugin",
+]
+
+[[package]]
+name = "prettyplease"
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2bfe0f4c752e450fc2faf62654f1c134747922825d5b04ca717b8874f41a40c0"
+dependencies = [
+ "proc-macro2",
+ "syn",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.107"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "985e7ec9bb745e6ce6535b544d84d6cd6f7ad8bd711c398938ae983b91a766d9"
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+ "unicode-ident",
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+[[package]]
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+checksum = "1fbf4db142a473a8d80c26bbf18454ed458bf8d26c8219c331daecfdbd079001"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8a7852d02fc848982e0c167ef163aaff9cd91dc640ba85e263cb1ce46fae51cd"
+
+[[package]]
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+checksum = "4148590afebada386688f18773da617792bf2ef03ffc1e4cbd2b1d45b023e0ba"
+dependencies = [
+ "serde_core",
+]
+
+[[package]]
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+checksum = "67dca2c9c51e58a4791a4b1ed58308b39c64224d349a935ab5039aa360942a48"
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+ "serde_derive",
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+
+[[package]]
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+ "proc-macro2",
+ "quote",
+ "syn",
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+ "itoa",
+ "memchr",
+ "serde",
+ "serde_core",
+ "zmij",
+]
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+[[package]]
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+checksum = "d78c8dee4c7bf0e14673097256fed6142ce9d3b85a408189d07482442145823b"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
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+checksum = "a2c754d6c33795a1c324727428e5a7dedb5b06195f9890bdbcba760d3e246563"
+
+[[package]]
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+checksum = "4495a6f85dd94c411c749303efcbc5defade0b0cbdbc0541495241ab917a9b5a"
+dependencies = [
+ "leb128fmt",
+ "wasmparser",
+]
+
+[[package]]
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+checksum = "c86ff6668190d9fb70372b306b4f9fe8930f0e2f57ce72e4922bf2f117900949"
+dependencies = [
+ "anyhow",
+ "indexmap",
+ "wasm-encoder",
+ "wasmparser",
+]
+
+[[package]]
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+checksum = "974d643b125b272607e2fff8012ea14a8328acd7621e4bafa7afb32500052b1b"
+dependencies = [
+ "bitflags",
+ "hashbrown",
+ "indexmap",
+ "semver",
+]
+
+[[package]]
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+checksum = "b85a987ab61d365382d25c7d47e26edd48941b3bf6e3fbf76eff918bc71dab06"
+dependencies = [
+ "bitflags",
+ "wit-bindgen-rust-macro",
+]
+
+[[package]]
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+ "anyhow",
+ "heck",
+ "wit-parser",
+]
+
+[[package]]
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+dependencies = [
+ "anyhow",
+ "heck",
+ "indexmap",
+ "prettyplease",
+ "syn",
+ "wasm-metadata",
+ "wit-bindgen-core",
+ "wit-component",
+]
+
+[[package]]
+name = "wit-bindgen-rust-macro"
+version = "0.63.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
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+dependencies = [
+ "anyhow",
+ "macro-string",
+ "prettyplease",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "wit-bindgen-core",
+ "wit-bindgen-rust",
+]
+
+[[package]]
+name = "wit-component"
+version = "0.262.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "078def49fdb49cab405c3006e05793b3fdaf7069126ba6b9c97d01ec8c98fe4c"
+dependencies = [
+ "anyhow",
+ "bitflags",
+ "indexmap",
+ "log",
+ "serde",
+ "serde_derive",
+ "serde_json",
+ "wasm-encoder",
+ "wasm-metadata",
+ "wasmparser",
+ "wit-parser",
+]
+
+[[package]]
+name = "wit-parser"
+version = "0.262.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "00f0dc051466ffe46787721fca3d088536f158ae400be044f1b1c386ba9397ad"
+dependencies = [
+ "anyhow",
+ "hashbrown",
+ "id-arena",
+ "indexmap",
+ "log",
+ "semver",
+ "serde",
+ "serde_derive",
+ "serde_json",
+ "unicode-ident",
+ "wasmparser",
+]
+
+[[package]]
+name = "zmij"
+version = "1.0.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "29666d0abbfad1e3dc4dcf6144730dd3a3ab225bbbdac83319345b1b44ccfc1b"
diff --git a/crates/ide-plugin/tests/fixtures/diagnostics/Cargo.toml b/crates/ide-plugin/tests/fixtures/diagnostics/Cargo.toml
new file mode 100644
index 000000000..3a1db6261
--- /dev/null
+++ b/crates/ide-plugin/tests/fixtures/diagnostics/Cargo.toml
@@ -0,0 +1,24 @@
+[package]
+name = "openidea-test-diagnostics"
+version = "0.1.0"
+edition = "2024"
+publish = false
+
+[workspace]
+
+[lib]
+crate-type = ["cdylib", "rlib"]
+
+[features]
+diagnostics-first = []
+diagnostics-last = []
+
+[dependencies]
+openidea-plugin = { path = "../../../../../sdk/rust/openidea-plugin" }
+
+[profile.release]
+opt-level = "s"
+lto = true
+strip = true
+codegen-units = 1
+panic = "abort"
diff --git a/crates/ide-plugin/tests/fixtures/diagnostics/README.md b/crates/ide-plugin/tests/fixtures/diagnostics/README.md
new file mode 100644
index 000000000..0b0214013
--- /dev/null
+++ b/crates/ide-plugin/tests/fixtures/diagnostics/README.md
@@ -0,0 +1,6 @@
+# Diagnostics provider fixture
+
+Build with `plugins/build.sh crates/ide-plugin/tests/fixtures/diagnostics`.
+Used by `cargo test -p ide-host --test plugin_diagnostics` for real Wasm dispatch,
+UTF-16 ranges, debouncing, cancellation, window/project lifecycle and coexistence
+with manually published diagnostics. Not a marketplace plugin.
diff --git a/crates/ide-plugin/tests/fixtures/diagnostics/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/diagnostics/dist/plugin.wasm
new file mode 100644
index 000000000..7473062ba
Binary files /dev/null and b/crates/ide-plugin/tests/fixtures/diagnostics/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/diagnostics/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/diagnostics/dist/plugin.wasm.sources
new file mode 100644
index 000000000..703a871f7
--- /dev/null
+++ b/crates/ide-plugin/tests/fixtures/diagnostics/dist/plugin.wasm.sources
@@ -0,0 +1 @@
+f757407f530839b8c43697e310926c5b141231bd8f2781ac92eee3a9de3f0f30
diff --git a/crates/ide-plugin/tests/fixtures/diagnostics/plugin.toml b/crates/ide-plugin/tests/fixtures/diagnostics/plugin.toml
new file mode 100644
index 000000000..e2c6cb522
--- /dev/null
+++ b/crates/ide-plugin/tests/fixtures/diagnostics/plugin.toml
@@ -0,0 +1,23 @@
+id = "test.diagnostics"
+name = "Diagnostics fixture"
+version = "0.1.0"
+engines.openidea = "^1.3"
+wasm = "dist/plugin.wasm"
+[capabilities]
+required = ["project.read"]
+
+[[contributes.providers]]
+kinds = ["diagnostics"]
+languages = ["text", "plaintext"]
+
+[[contributes.commands]]
+id = "publish"
+title = "Publish fixture diagnostic"
+
+[[contributes.commands]]
+id = "calls"
+title = "Diagnostics fixture call count"
+
+[[contributes.commands]]
+id = "wait"
+title = "Wait for diagnostics fixture"
diff --git a/crates/ide-plugin/tests/fixtures/diagnostics/src/lib.rs b/crates/ide-plugin/tests/fixtures/diagnostics/src/lib.rs
new file mode 100644
index 000000000..98cba1505
--- /dev/null
+++ b/crates/ide-plugin/tests/fixtures/diagnostics/src/lib.rs
@@ -0,0 +1,169 @@
+use openidea_plugin::diagnostics::{DiagnosticsProvider, Document};
+use openidea_plugin::{Diagnostic, Error, Invocation, Plugin, Range, Severity, host, register_plugin, text};
+use std::time::Duration;
+
+#[derive(Default)]
+struct Fixture {
+    calls: u64,
+}
+
+impl Plugin for Fixture {
+    fn run_command(&mut self, id: &str, _: &Invocation, arg: Option<&str>) -> Result<Option<String>, Error> {
+        match id {
+            "wait" => {
+                std::thread::sleep(Duration::from_millis(400));
+                Ok(Some("finished".into()))
+            }
+            "calls" => Ok(Some(self.calls.to_string())),
+            "publish" => host::publish_diagnostics(
+                arg.unwrap_or_default(),
+                &[Diagnostic::new(Range::default(), Severity::Info, "Manual problem")],
+            )
+            .map(|()| None),
+            _ => Err(Error::NotFound(id.into())),
+        }
+    }
+}
+
+impl DiagnosticsProvider for Fixture {
+    fn diagnostics(&mut self, doc: &Document) -> Vec<Diagnostic> {
+        self.calls += 1;
+        if doc.text == "limits" {
+            let mut diagnostic = Diagnostic::new(Range::default(), Severity::Hint, "m".repeat(5000));
+            diagnostic.source = Some("s".repeat(200));
+            diagnostic.code = Some("c".repeat(200));
+            diagnostic.unnecessary = true;
+            diagnostic.deprecated = true;
+            return vec![diagnostic; 5001];
+        }
+        if doc.text.starts_with("slow") {
+            std::thread::sleep(Duration::from_millis(200));
+        }
+        if doc.text.starts_with("spin") {
+            loop {
+                std::hint::spin_loop();
+            }
+        }
+        if doc.text.starts_with("panic") {
+            panic!("diagnostics fixture failed");
+        }
+        doc.text
+            .match_indices("BAD")
+            .map(|(offset, _)| {
+                Diagnostic::new(
+                    Range { start: text::position(&doc.text, offset), end: text::position(&doc.text, offset + 3) },
+                    Severity::Warning,
+                    format!("BAD in {} at version {}", doc.language, doc.version),
+                )
+                .code("bad-word")
+            })
+            .collect()
+    }
+}
+
+impl openidea_plugin::hover::HoverProvider for Fixture {
+    fn hover(&mut self, _: &Document, _: openidea_plugin::Position) -> Option<openidea_plugin::hover::Hover> {
+        None
+    }
+}
+
+impl openidea_plugin::inlay_hints::InlayHints for Fixture {
+    fn inlay_hints(&mut self, _: &Document, _: Range) -> Vec<openidea_plugin::inlay_hints::InlayHint> {
+        Vec::new()
+    }
+}
+
+impl openidea_plugin::providers::Providers for Fixture {}
+
+impl openidea_plugin::endpoints::EndpointsProvider for Fixture {
+    fn endpoints(&mut self, _: &Invocation) -> Result<Vec<openidea_plugin::endpoints::Endpoint>, Error> {
+        Ok(Vec::new())
+    }
+}
+
+impl openidea_plugin::views::Views for Fixture {
+    fn render(
+        &mut self,
+        _: &str,
+        _: Option<openidea_plugin::views::Viewport>,
+        _: &Invocation,
+    ) -> Result<openidea_plugin::views::View, Error> {
+        Ok(openidea_plugin::views::View::message(""))
+    }
+}
+
+impl openidea_plugin::indexing::DocumentIndexer for Fixture {
+    fn index(&mut self, _: &openidea_plugin::indexing::Document) -> openidea_plugin::indexing::Edges {
+        openidea_plugin::indexing::Edges::default()
+    }
+}
+
+impl openidea_plugin::syntax::SyntaxProvider for Fixture {
+    fn highlights(&mut self, _: &str, _: &str) -> Vec<openidea_plugin::syntax::Token> {
+        Vec::new()
+    }
+}
+
+impl openidea_plugin::semantic_tokens::SemanticTokens for Fixture {
+    fn semantic_tokens(&mut self, _: &Document) -> Vec<openidea_plugin::semantic_tokens::SemanticToken> {
+        Vec::new()
+    }
+}
+
+impl openidea_plugin::details::Details for Fixture {
+    fn detail(&mut self, _: &str, _: &str, _: &Invocation) -> Result<Vec<openidea_plugin::details::Tab>, Error> {
+        Ok(Vec::new())
+    }
+}
+
+impl openidea_plugin::commit::CommitChecks for Fixture {
+    fn check(
+        &mut self,
+        _: &str,
+        _: &openidea_plugin::CommitDraft,
+        _: &Invocation,
+    ) -> Result<Vec<openidea_plugin::commit::CommitProblem>, Error> {
+        Ok(Vec::new())
+    }
+}
+
+impl openidea_plugin::file_actions::FileActions for Fixture {
+    fn file_actions(&mut self, _: &Document, _: Range) -> Vec<openidea_plugin::file_actions::FileAction> {
+        Vec::new()
+    }
+}
+
+#[cfg(feature = "diagnostics-first")]
+register_plugin!(
+    Fixture,
+    diagnostics,
+    endpoints,
+    views,
+    indexing,
+    syntax,
+    semantic_tokens,
+    hover,
+    providers,
+    inlay_hints,
+    details,
+    commit_checks,
+    file_actions
+);
+#[cfg(all(feature = "diagnostics-last", not(feature = "diagnostics-first")))]
+register_plugin!(
+    Fixture,
+    file_actions,
+    commit_checks,
+    details,
+    inlay_hints,
+    providers,
+    hover,
+    semantic_tokens,
+    syntax,
+    indexing,
+    views,
+    endpoints,
+    diagnostics
+);
+#[cfg(not(any(feature = "diagnostics-first", feature = "diagnostics-last")))]
+register_plugin!(Fixture, diagnostics);
diff --git a/crates/ide-plugin/tests/fixtures/endpoints/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/endpoints/dist/plugin.wasm
index 752d3d658..36143132c 100644
Binary files a/crates/ide-plugin/tests/fixtures/endpoints/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/endpoints/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/endpoints/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/endpoints/dist/plugin.wasm.sources
index 52a837bcc..607ce0ede 100644
--- a/crates/ide-plugin/tests/fixtures/endpoints/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/endpoints/dist/plugin.wasm.sources
@@ -1 +1 @@
-cdd58d817f507452ed192e3a19071bd56740efc70c4a965b0d48e5b224fff1d4
+99cba883e8030d7679db366a4b18b8c456afccbcbc949e0d7411adc6411f2e00
diff --git a/crates/ide-plugin/tests/fixtures/file-templates/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/file-templates/dist/plugin.wasm
index 4e214ba73..7ab317e3e 100644
Binary files a/crates/ide-plugin/tests/fixtures/file-templates/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/file-templates/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/file-templates/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/file-templates/dist/plugin.wasm.sources
index 6d3cc157b..ffe9e0945 100644
--- a/crates/ide-plugin/tests/fixtures/file-templates/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/file-templates/dist/plugin.wasm.sources
@@ -1 +1 @@
-44da806d4e0d4d370534d108bd90406bcc475bac17cf69d0d323d341b79deb9a
+afcf583238dddd20d0d709ce7619fada0e60916f9e3c039569d37dec75354471
diff --git a/crates/ide-plugin/tests/fixtures/grouped-views/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/grouped-views/dist/plugin.wasm
index 5db3f2dc7..aeb1692c6 100644
Binary files a/crates/ide-plugin/tests/fixtures/grouped-views/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/grouped-views/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/grouped-views/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/grouped-views/dist/plugin.wasm.sources
index fedec7ba4..1944ef030 100644
--- a/crates/ide-plugin/tests/fixtures/grouped-views/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/grouped-views/dist/plugin.wasm.sources
@@ -1 +1 @@
-6d61b436c76c26b7edf444c89c8e71091ca7c5bccfba9ae79e770f70f8b9013d
+a1ce41144630be398bb63cffca26005955de0511a17c71dc286e7762b19e9cab
diff --git a/crates/ide-plugin/tests/fixtures/hello/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/hello/dist/plugin.wasm
index 046be4056..515fdea7d 100644
Binary files a/crates/ide-plugin/tests/fixtures/hello/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/hello/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/hello/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/hello/dist/plugin.wasm.sources
index 2d8db8996..c4aef7756 100644
--- a/crates/ide-plugin/tests/fixtures/hello/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/hello/dist/plugin.wasm.sources
@@ -1 +1 @@
-b4fedecefcc934cd6ddc49c3ffe948468a7603930a47c3594be85f5f01758fab
+bbfc134f2121f301bbbcb0f0d596d7b3cc059455bba5ca78992e8bfa6630ce42
diff --git a/crates/ide-plugin/tests/fixtures/hover/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/hover/dist/plugin.wasm
index 70d531824..46b0d9891 100644
Binary files a/crates/ide-plugin/tests/fixtures/hover/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/hover/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/hover/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/hover/dist/plugin.wasm.sources
index 242254d86..dab679e29 100644
--- a/crates/ide-plugin/tests/fixtures/hover/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/hover/dist/plugin.wasm.sources
@@ -1 +1 @@
-e593cd53d3757c3a738121ec2fcc3840a9d1c0dcc6ea1e17134c9d53ef695ebc
+b7f45420859ce9540e0aae1fd803eee13529ef63d0a2f0b6ba9e43a5958eb457
diff --git a/crates/ide-plugin/tests/fixtures/indexer/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/indexer/dist/plugin.wasm
index f4c49c9cb..e4b6a360d 100644
Binary files a/crates/ide-plugin/tests/fixtures/indexer/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/indexer/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/indexer/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/indexer/dist/plugin.wasm.sources
index 4165bb01d..c1d45840b 100644
--- a/crates/ide-plugin/tests/fixtures/indexer/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/indexer/dist/plugin.wasm.sources
@@ -1 +1 @@
-3f49e3bb7f523103f70a39087e96500b5cd806ab60de60fceb480ca54ad4aa1d
+041aa03873ff1d8133f181e86aab2ad3fda41e46503886754114f3abef3643da
diff --git a/crates/ide-plugin/tests/fixtures/inlay-hints/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/inlay-hints/dist/plugin.wasm
index 4b3f14ace..ecce5ea24 100644
Binary files a/crates/ide-plugin/tests/fixtures/inlay-hints/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/inlay-hints/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/inlay-hints/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/inlay-hints/dist/plugin.wasm.sources
index 8c1c7456b..d29297306 100644
--- a/crates/ide-plugin/tests/fixtures/inlay-hints/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/inlay-hints/dist/plugin.wasm.sources
@@ -1 +1 @@
-f3290c6ef1e794c95d3e8993aacecd58566e2ba690f966f52613a2dbdfa21dd5
+edcad61ab8e71cff2297edd9b902359d76ef04446bdfc42aae34420ced4d7f26
diff --git a/crates/ide-plugin/tests/fixtures/jobs/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/jobs/dist/plugin.wasm
index 2400a6300..db5abfe11 100644
Binary files a/crates/ide-plugin/tests/fixtures/jobs/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/jobs/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/jobs/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/jobs/dist/plugin.wasm.sources
index ef1c5a1f9..20511645d 100644
--- a/crates/ide-plugin/tests/fixtures/jobs/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/jobs/dist/plugin.wasm.sources
@@ -1 +1 @@
-7e95ef2102982c48740d664cf050c86d2f7015d438e30376c35c5a97c2fb8c1b
+aad3a25c3522fbff6f48c0c1e9de23b6d0d5361ba6658b744ad1590e9fdbe255
diff --git a/crates/ide-plugin/tests/fixtures/misbehave/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/misbehave/dist/plugin.wasm.sources
index 2c433f90d..8f1030378 100644
--- a/crates/ide-plugin/tests/fixtures/misbehave/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/misbehave/dist/plugin.wasm.sources
@@ -1 +1 @@
-58bcfb533bf386c0f0179e6775be834aa2d30f1b5e88e7ca00ad662bdd35699e
+cfb432ea8943bf9b7e2f3ad3708df35260eebd04b3ac059c7643b378a35cd036
diff --git a/crates/ide-plugin/tests/fixtures/path-events/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/path-events/dist/plugin.wasm
index 85c41c477..bedbb1f37 100644
Binary files a/crates/ide-plugin/tests/fixtures/path-events/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/path-events/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/path-events/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/path-events/dist/plugin.wasm.sources
index 3af778b65..ab0768e5b 100644
--- a/crates/ide-plugin/tests/fixtures/path-events/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/path-events/dist/plugin.wasm.sources
@@ -1 +1 @@
-12e92a08e3493a282b811592d1f044f293d6296b36b4c8e3b25ef80c5aca022f
+82f53a3f36f965c76575a08609439e0bc9cea37f1aef7cc1671e9ec72a17f120
diff --git a/crates/ide-plugin/tests/fixtures/semantic-tokens/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/semantic-tokens/dist/plugin.wasm
index 126b88723..45c9f6afa 100644
Binary files a/crates/ide-plugin/tests/fixtures/semantic-tokens/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/semantic-tokens/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/semantic-tokens/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/semantic-tokens/dist/plugin.wasm.sources
index 2b0fb51d6..d6ad006c7 100644
--- a/crates/ide-plugin/tests/fixtures/semantic-tokens/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/semantic-tokens/dist/plugin.wasm.sources
@@ -1 +1 @@
-eb481d1624b5d96488925f15dfa773a74c38cde490bc0c43b9a8caf6631168ce
+a8d40f2224246e81e015d576a5fa70e83779af9fade614d61212b33fbb0961e9
diff --git a/crates/ide-plugin/tests/fixtures/storage/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/storage/dist/plugin.wasm
index acb7a86ff..88b217dd1 100644
Binary files a/crates/ide-plugin/tests/fixtures/storage/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/storage/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/storage/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/storage/dist/plugin.wasm.sources
index 05e8a7da9..7a222a646 100644
--- a/crates/ide-plugin/tests/fixtures/storage/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/storage/dist/plugin.wasm.sources
@@ -1 +1 @@
-99e6543b156c2ea1a916f597224416db55f10bdce37af8943e2297a397fad0c9
+e60bcf1e179f6485e14de3755907c93344ef3cdf8158f01bea84343858ba7434
diff --git a/crates/ide-plugin/tests/fixtures/symbols/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/symbols/dist/plugin.wasm
index f1ad28ffa..0ee2946c0 100644
Binary files a/crates/ide-plugin/tests/fixtures/symbols/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/symbols/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/symbols/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/symbols/dist/plugin.wasm.sources
index 4173f7d66..36454c216 100644
--- a/crates/ide-plugin/tests/fixtures/symbols/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/symbols/dist/plugin.wasm.sources
@@ -1 +1 @@
-be318451a7ea7653bfd40a5624aa0951b4fb814c8c39a494ed3066c7ac8ef35e
+5cadc40061284bd5573f8323b02fb7ea7be18eb4323978b3f0b39337a9896774
diff --git a/crates/ide-plugin/tests/fixtures/tables/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/tables/dist/plugin.wasm
index d54eaa4eb..4f1227e4b 100644
Binary files a/crates/ide-plugin/tests/fixtures/tables/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/tables/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/tables/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/tables/dist/plugin.wasm.sources
index 1ee2e8c2d..ca8391d43 100644
--- a/crates/ide-plugin/tests/fixtures/tables/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/tables/dist/plugin.wasm.sources
@@ -1 +1 @@
-9b4b83d13abbfaf88b04dff3ecc1beca7f12805fa651b53f1087b6e4ff2f0e38
+5377825f5801850d6ed7ec989f6e954fae477d81cd3ce0d5a2b8baeb9febcf74
diff --git a/crates/ide-plugin/tests/fixtures/web-log/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/web-log/dist/plugin.wasm
index dba2d159c..b1bf544b1 100644
Binary files a/crates/ide-plugin/tests/fixtures/web-log/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/web-log/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/web-log/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/web-log/dist/plugin.wasm.sources
index 7276e0e76..4fc2bc467 100644
--- a/crates/ide-plugin/tests/fixtures/web-log/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/web-log/dist/plugin.wasm.sources
@@ -1 +1 @@
-74acb8ab9079c558a120c145319f01b54294cbf6fa4cbd33907a0d58e1ef2906
+e1414e522a45066616475fae229c4dade82ba16eedef49aac8d4c014522a0684
diff --git a/crates/ide-plugin/tests/fixtures/web-pty/dist/plugin.wasm b/crates/ide-plugin/tests/fixtures/web-pty/dist/plugin.wasm
index 2255d5579..56833ae13 100644
Binary files a/crates/ide-plugin/tests/fixtures/web-pty/dist/plugin.wasm and b/crates/ide-plugin/tests/fixtures/web-pty/dist/plugin.wasm differ
diff --git a/crates/ide-plugin/tests/fixtures/web-pty/dist/plugin.wasm.sources b/crates/ide-plugin/tests/fixtures/web-pty/dist/plugin.wasm.sources
index c1cf5b704..2ac9c8016 100644
--- a/crates/ide-plugin/tests/fixtures/web-pty/dist/plugin.wasm.sources
+++ b/crates/ide-plugin/tests/fixtures/web-pty/dist/plugin.wasm.sources
@@ -1 +1 @@
-bb6e1eba6b9f28ca769bee0c6dad9ceab536d486efcbe0ad56bbfe621e2d7679
+5a50246a300a15c8b9e50457094442fe35f0efe1534feb6f5cb407e052404c07
diff --git a/plugins/README.md b/plugins/README.md
index c9280906b..9f01c55f7 100644
--- a/plugins/README.md
+++ b/plugins/README.md
@@ -566,7 +566,7 @@ declaration matches the file's language are called (and loaded):
 
 ```toml
 [[contributes.providers]]
-kinds = ["definition", "line-markers", "completion"]  # also "inline-completion", "code-actions", "semantic-tokens", "hover", "inlay-hints"
+kinds = ["definition", "line-markers", "completion"]  # also "inline-completion", "code-actions", "semantic-tokens", "hover", "inlay-hints", "diagnostics"
 languages = ["java", "xml"]                           # editor language ids; "*" for any
 ```
 
@@ -676,6 +676,54 @@ edit-path budget, and shows the server's hover first, then each plugin's
 below a rule. `range`, when given, is the text the hover describes (used when
 the server names none). At most 64 KiB of Markdown per plugin.
 
+#### Diagnostics while typing
+
+The `diagnostics` kind (API 1.3) checks unsaved documents in its declared
+`languages` (`"*"` matches any language). Implement
+`openidea_plugin::diagnostics::DiagnosticsProvider` and register with
+`register_plugin!(MyPlugin, diagnostics)`:
+
+```rust
+impl DiagnosticsProvider for MyPlugin {
+    fn diagnostics(&mut self, doc: &Document) -> Vec<Diagnostic> {
+        // doc.path is absolute; doc.language is the editor language id.
+        // doc.version identifies this snapshot; doc.text includes unsaved edits.
+        check(&doc.text)
+    }
+}
+```
+
+The optional WIT export is `diagnostics-provider.diagnostics(document) ->
+list<diagnostic>` in worlds `plugin-diagnostics` / `editor-diagnostics`. It uses the
+same diagnostic record as `diagnostics.publish`, including 0-based UTF-16
+ranges. The export-only world uses `editor-diagnostics` because `diagnostics`
+already names the released host interface. The provider declaration supplies the current document without an
+additional capability; host imports keep their usual capability checks
+(`publish` still requires `project.read`). Providers run without an interactive
+invocation, so they cannot open prompts or write to the active editor.
+
+The host requests diagnostics about 300 ms after opening a document or after
+its latest edit, under the editor-provider budget (normally 50 ms soft /
+500 ms hard). It snapshots the buffer in the background, cancels superseded
+requests, and drops older document versions. Documents over 2 MiB and virtual
+library documents are excluded. Return an empty list to remove provider
+problems. At most 5,000 diagnostics are retained per provider and document;
+messages are limited to 4 KiB, source/code to 128 bytes.
+
+Provider problems and manually published problems use separate producers,
+`plugin-provider:<plugin-id>` and `plugin:<plugin-id>`, and both appear alongside
+language-server diagnostics. Each producer replaces only its own results.
+Closing the document/project or disabling, uninstalling, reloading or failing
+the plugin clears provider results. A reclaimed idle instance keeps its results
+until the next request. Requests and results stay with the originating project
+and window, including when two windows edit the same path differently. Project
+plugins receive documents only from the project where they were granted.
+
+Native plugin tests can use `MockHost::refresh_diagnostics(&mut provider)` to
+check the current versioned mock editor and `provider_diagnostics()` to inspect
+its answers separately from `diagnostics()` (manual publishing). The mock call
+is explicit; debounce and cancellation are exercised by the real Wasm host tests.
+
 #### Inlay hints
 
 The `inlay-hints` kind (API 1.3) shows short labels inside the code of
diff --git a/plugins/official/ai-completion/dist/plugin.wasm b/plugins/official/ai-completion/dist/plugin.wasm
index 867eac614..9c757fa70 100644
Binary files a/plugins/official/ai-completion/dist/plugin.wasm and b/plugins/official/ai-completion/dist/plugin.wasm differ
diff --git a/plugins/official/ai-completion/dist/plugin.wasm.sources b/plugins/official/ai-completion/dist/plugin.wasm.sources
index b33b8927d..45a3177f5 100644
--- a/plugins/official/ai-completion/dist/plugin.wasm.sources
+++ b/plugins/official/ai-completion/dist/plugin.wasm.sources
@@ -1 +1 @@
-f5d442002dd3315f14ed7ebe873a7d1c858fa31a2840aebc7876366269d5fd6c
+61aaa8563701c6d4c147eaef87363ac0600c79fd9ef2ee8c8c1cc9c7e56794ed
diff --git a/plugins/official/checkstyle/dist/plugin.wasm b/plugins/official/checkstyle/dist/plugin.wasm
index bbd70c1ae..7ee505e91 100644
Binary files a/plugins/official/checkstyle/dist/plugin.wasm and b/plugins/official/checkstyle/dist/plugin.wasm differ
diff --git a/plugins/official/checkstyle/dist/plugin.wasm.sources b/plugins/official/checkstyle/dist/plugin.wasm.sources
index cb4c66f56..1d3b7f8d1 100644
--- a/plugins/official/checkstyle/dist/plugin.wasm.sources
+++ b/plugins/official/checkstyle/dist/plugin.wasm.sources
@@ -1 +1 @@
-0bebf24cc46dd2dac9c51fffcd4b9186f7e575c2d552e8d600c02fa5fe8fa9b0
+ab0a7b4daf59fda5938b10c42628bb141c94bc0d82464254a6b0157d74e98477
diff --git a/plugins/official/csv-editor/dist/plugin.wasm b/plugins/official/csv-editor/dist/plugin.wasm
index 0212da992..73d269c44 100644
Binary files a/plugins/official/csv-editor/dist/plugin.wasm and b/plugins/official/csv-editor/dist/plugin.wasm differ
diff --git a/plugins/official/csv-editor/dist/plugin.wasm.sources b/plugins/official/csv-editor/dist/plugin.wasm.sources
index b4b5ddbaf..a614ca79b 100644
--- a/plugins/official/csv-editor/dist/plugin.wasm.sources
+++ b/plugins/official/csv-editor/dist/plugin.wasm.sources
@@ -1 +1 @@
-a4179ed839602e1d1697d738689d8936d22889b0d4e09ff953d6354a6d91f368
+5813b46ce5ec12b9ca4bdfe61d49c63ed1af736238398a1c2e03ca7c3633469c
diff --git a/plugins/official/git-toolbox/dist/plugin.wasm b/plugins/official/git-toolbox/dist/plugin.wasm
index 74356cd81..0c36535b3 100644
Binary files a/plugins/official/git-toolbox/dist/plugin.wasm and b/plugins/official/git-toolbox/dist/plugin.wasm differ
diff --git a/plugins/official/git-toolbox/dist/plugin.wasm.sources b/plugins/official/git-toolbox/dist/plugin.wasm.sources
index cdb84bef7..20f4d1921 100644
--- a/plugins/official/git-toolbox/dist/plugin.wasm.sources
+++ b/plugins/official/git-toolbox/dist/plugin.wasm.sources
@@ -1 +1 @@
-eb5f3a257f2551a29c3ad62b222b0641b07b7b9422780e1ffecafa7e39b5032d
+208cf58ff413f2ef75abfd0a4280d6e38393acf4e2d0a30f9c4d3294aa9ec82f
diff --git a/plugins/official/graphviz/dist/plugin.wasm b/plugins/official/graphviz/dist/plugin.wasm
index b2bbb9817..7a4b88b6a 100644
Binary files a/plugins/official/graphviz/dist/plugin.wasm and b/plugins/official/graphviz/dist/plugin.wasm differ
diff --git a/plugins/official/graphviz/dist/plugin.wasm.sources b/plugins/official/graphviz/dist/plugin.wasm.sources
index a75fb7800..e446da7d9 100644
--- a/plugins/official/graphviz/dist/plugin.wasm.sources
+++ b/plugins/official/graphviz/dist/plugin.wasm.sources
@@ -1 +1 @@
-74df219fa8bfbb491bc2f3c021e3df2a8daa9bed03606e8d558624918d9d7104
+f83c2371ee5dd6c9d8d027ec3515fb7850141ac694d873ef0463a64ec6edcc9d
diff --git a/plugins/official/key-promoter/dist/plugin.wasm b/plugins/official/key-promoter/dist/plugin.wasm
index 9baa571db..e54ae18c3 100644
Binary files a/plugins/official/key-promoter/dist/plugin.wasm and b/plugins/official/key-promoter/dist/plugin.wasm differ
diff --git a/plugins/official/key-promoter/dist/plugin.wasm.sources b/plugins/official/key-promoter/dist/plugin.wasm.sources
index f1891d7a6..d1dfe3ad8 100644
--- a/plugins/official/key-promoter/dist/plugin.wasm.sources
+++ b/plugins/official/key-promoter/dist/plugin.wasm.sources
@@ -1 +1 @@
-19c90c5f90d6a26be8f4762d42cbe2f9281e311acc61467bd104da7ec25e5545
+f5baecb3f80efee4244bc096039ae7ac926c8bc73eb08fdfe5ecf81a4e2c38c9
diff --git a/plugins/official/license-header/dist/plugin.wasm b/plugins/official/license-header/dist/plugin.wasm
index 3a78025b9..fa235c304 100644
Binary files a/plugins/official/license-header/dist/plugin.wasm and b/plugins/official/license-header/dist/plugin.wasm differ
diff --git a/plugins/official/license-header/dist/plugin.wasm.sources b/plugins/official/license-header/dist/plugin.wasm.sources
index 6b9d7a3ea..e10cba55a 100644
--- a/plugins/official/license-header/dist/plugin.wasm.sources
+++ b/plugins/official/license-header/dist/plugin.wasm.sources
@@ -1 +1 @@
-a9bf8c6074ffb5d5335f07d6e5f1af6108faec0ca6e282a85684b991995baefc
+e4f62cf323d7186dcdc2972b0330086bc6279dcdc884d1997a84c1a589e739f8
diff --git a/plugins/official/mybatis/dist/plugin.wasm b/plugins/official/mybatis/dist/plugin.wasm
index b17ee3ee3..2141ea7bb 100644
Binary files a/plugins/official/mybatis/dist/plugin.wasm and b/plugins/official/mybatis/dist/plugin.wasm differ
diff --git a/plugins/official/mybatis/dist/plugin.wasm.sources b/plugins/official/mybatis/dist/plugin.wasm.sources
index 9fb0a4cd6..ab575d7fa 100644
--- a/plugins/official/mybatis/dist/plugin.wasm.sources
+++ b/plugins/official/mybatis/dist/plugin.wasm.sources
@@ -1 +1 @@
-6519aa645fe62c9f963d1baf7cd0a36dd75787b37da46a7d1218f3983f828e79
+216af779424458d3fe4de470f2358f21ebc15d62be3d285f59cba19d61e59f3d
diff --git a/plugins/official/regex-tester/dist/plugin.wasm b/plugins/official/regex-tester/dist/plugin.wasm
index 276daf1e8..49293a0f5 100644
Binary files a/plugins/official/regex-tester/dist/plugin.wasm and b/plugins/official/regex-tester/dist/plugin.wasm differ
diff --git a/plugins/official/regex-tester/dist/plugin.wasm.sources b/plugins/official/regex-tester/dist/plugin.wasm.sources
index d5ee8b74c..004411fe4 100644
--- a/plugins/official/regex-tester/dist/plugin.wasm.sources
+++ b/plugins/official/regex-tester/dist/plugin.wasm.sources
@@ -1 +1 @@
-a95e6ff3977bf25cf106f6641cd8333124bb8615a8c327baefa068e36dd3d2ee
+b2994bcb35737abbd001535308fcd4d3f0bab4cd61e580d8af1312451e760fe3
diff --git a/plugins/official/solidity/dist/plugin.wasm b/plugins/official/solidity/dist/plugin.wasm
index a9fc62c52..a0e8bdf89 100644
Binary files a/plugins/official/solidity/dist/plugin.wasm and b/plugins/official/solidity/dist/plugin.wasm differ
diff --git a/plugins/official/solidity/dist/plugin.wasm.sources b/plugins/official/solidity/dist/plugin.wasm.sources
index 956a79eb4..11794ff4d 100644
--- a/plugins/official/solidity/dist/plugin.wasm.sources
+++ b/plugins/official/solidity/dist/plugin.wasm.sources
@@ -1 +1 @@
-674e164012c93a106a0c3977b1066d5a49524f8f8426fb09404e3b7a7340a629
+6d5d5b09fd48e9b48891a91b3dd13f9d0d2f1771685a549c683295370233ae17
diff --git a/plugins/official/string-tools/dist/plugin.wasm b/plugins/official/string-tools/dist/plugin.wasm
index 647a81967..6ec0dd65a 100644
Binary files a/plugins/official/string-tools/dist/plugin.wasm and b/plugins/official/string-tools/dist/plugin.wasm differ
diff --git a/plugins/official/string-tools/dist/plugin.wasm.sources b/plugins/official/string-tools/dist/plugin.wasm.sources
index 45439d0f3..21885e1c9 100644
--- a/plugins/official/string-tools/dist/plugin.wasm.sources
+++ b/plugins/official/string-tools/dist/plugin.wasm.sources
@@ -1 +1 @@
-f253276316839b418223b8292683e313d311ce41c9701c04c9c3fcc85e0638e5
+5e6457d34c922284779cdcc42455ed1df9ed8b9245793134be566dcd3c8aab93
diff --git a/sdk/rust/openidea-plugin/README.md b/sdk/rust/openidea-plugin/README.md
index 9cde23a80..67811d0f0 100644
--- a/sdk/rust/openidea-plugin/README.md
+++ b/sdk/rust/openidea-plugin/README.md
@@ -14,6 +14,23 @@ and the [minimal fixture](../../../crates/ide-plugin/tests/fixtures/web-pty).
 The frame cannot access IPC directly. Its sessions belong to that frame and
 end with its view or plugin. There is no new WIT import for this API.
 
+API 1.3 also adds diagnostics for unsaved documents. Declare
+`kinds = ["diagnostics"]` and the supported `languages` under
+`[[contributes.providers]]`, implement
+`openidea_plugin::diagnostics::DiagnosticsProvider`, and export it with
+`register_plugin!(MyPlugin, diagnostics)`. The host supplies versioned text
+after a 300 ms debounce, cancels superseded calls, and drops stale answers
+under the editor-provider budget. Ranges use 0-based UTF-16 positions.
+
+The provider declaration supplies the document; host imports retain their
+usual capability checks. Provider results coexist with manually published
+diagnostics and are cleared with the document, project or plugin. Native
+tests can call `MockHost::refresh_diagnostics` and inspect
+`MockHost::provider_diagnostics`.
+
+See [the diagnostics contract and limits](../../../plugins/README.md#diagnostics-while-typing)
+and the [real Wasm fixture](../../../crates/ide-plugin/tests/fixtures/diagnostics).
+
 API 1.3 also adds `open-log-tab` to the web bridge: a generic read-only editor
 tab streams output from a granted process, with plugin-defined argument toggles.
 It uses the same backend authorization and bounded PTY transport. See the
diff --git a/sdk/rust/openidea-plugin/src/diagnostics.rs b/sdk/rust/openidea-plugin/src/diagnostics.rs
new file mode 100644
index 000000000..06b9a6e10
--- /dev/null
+++ b/sdk/rust/openidea-plugin/src/diagnostics.rs
@@ -0,0 +1,46 @@
+//! Diagnostics for unsaved documents. Declare `kinds = ["diagnostics"]` and
+//! register with `register_plugin!(MyPlugin, diagnostics)` (API 1.3).
+pub use crate::providers::Document;
+pub use crate::types::Diagnostic;
+
+pub trait DiagnosticsProvider {
+    fn diagnostics(&mut self, doc: &Document) -> Vec<Diagnostic>;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{Range, Severity, host, mock::MockHost};
+
+    struct Provider;
+    impl DiagnosticsProvider for Provider {
+        fn diagnostics(&mut self, doc: &Document) -> Vec<Diagnostic> {
+            vec![Diagnostic::new(
+                Range::default(),
+                Severity::Warning,
+                format!("{}:{}:{}", doc.language, doc.version, doc.text),
+            )]
+        }
+    }
+
+    #[test]
+    fn the_mock_uses_unsaved_versioned_text_and_keeps_manual_problems() {
+        let mock = MockHost::install();
+        mock.open_editor("/project/a.txt", "text", "a", &[]);
+        host::publish_diagnostics("/project/a.txt", &[Diagnostic::new(Range::default(), Severity::Info, "manual")])
+            .unwrap();
+        mock.type_in_editor("😀");
+        mock.refresh_diagnostics(&mut Provider);
+        assert_eq!(mock.provider_diagnostics()["/project/a.txt"][0].message, "text:2:a😀");
+        assert_eq!(mock.diagnostics()["/project/a.txt"][0].message, "manual");
+    }
+
+    #[test]
+    fn a_provider_needs_no_extra_capability_but_publishing_still_does() {
+        let mock = MockHost::install().with_capabilities(&[]);
+        mock.open_editor("/project/a.txt", "text", "unsaved", &[]);
+        mock.refresh_diagnostics(&mut Provider);
+        assert_eq!(mock.provider_diagnostics()["/project/a.txt"][0].message, "text:1:unsaved");
+        assert!(host::publish_diagnostics("/project/a.txt", &[]).is_err());
+    }
+}
diff --git a/sdk/rust/openidea-plugin/src/host.rs b/sdk/rust/openidea-plugin/src/host.rs
index 8f84d945a..3e5f06ec3 100644
--- a/sdk/rust/openidea-plugin/src/host.rs
+++ b/sdk/rust/openidea-plugin/src/host.rs
@@ -377,39 +377,40 @@ mod imp {
         wit::fs::write_bytes(path, bytes).map_err(error)
     }
 
-    pub fn publish_diagnostics(path: &str, items: &[Diagnostic]) -> Result<(), Error> {
+    pub fn diagnostic_to(d: &Diagnostic) -> wit::diagnostics::Diagnostic {
         use wit::diagnostics::{Diagnostic as D, RelatedInformation as R, Severity as S};
-        let items: Vec<D> = items
-            .iter()
-            .map(|d| D {
-                range: range_out(d.range),
-                severity: match d.severity {
-                    Severity::Error => S::Error,
-                    Severity::Warning => S::Warning,
-                    Severity::Info => S::Info,
-                    Severity::Hint => S::Hint,
-                },
-                message: d.message.clone(),
-                code: d.code.clone(),
-                source: d.source.clone(),
-                tags: [(d.unnecessary, "unnecessary"), (d.deprecated, "deprecated")]
-                    .into_iter()
-                    .filter(|(on, _)| *on)
-                    .map(|(_, tag)| tag.to_owned())
-                    .collect(),
-                related: d
-                    .related
-                    .iter()
-                    .map(|r| R {
-                        location: wit::types::Location {
-                            path: r.location.path.clone(),
-                            range: range_out(r.location.range),
-                        },
-                        message: r.message.clone(),
-                    })
-                    .collect(),
-            })
-            .collect();
+        D {
+            range: range_out(d.range),
+            severity: match d.severity {
+                Severity::Error => S::Error,
+                Severity::Warning => S::Warning,
+                Severity::Info => S::Info,
+                Severity::Hint => S::Hint,
+            },
+            message: d.message.clone(),
+            code: d.code.clone(),
+            source: d.source.clone(),
+            tags: [(d.unnecessary, "unnecessary"), (d.deprecated, "deprecated")]
+                .into_iter()
+                .filter(|(on, _)| *on)
+                .map(|(_, tag)| tag.to_owned())
+                .collect(),
+            related: d
+                .related
+                .iter()
+                .map(|r| R {
+                    location: wit::types::Location {
+                        path: r.location.path.clone(),
+                        range: range_out(r.location.range),
+                    },
+                    message: r.message.clone(),
+                })
+                .collect(),
+        }
+    }
+
+    pub fn publish_diagnostics(path: &str, items: &[Diagnostic]) -> Result<(), Error> {
+        let items: Vec<_> = items.iter().map(diagnostic_to).collect();
         wit::diagnostics::publish(path, &items).map_err(error)
     }
 
@@ -1141,3 +1142,9 @@ pub fn notify_with_actions(
 ) -> Result<(), Error> {
     imp::notify_with_actions(level, title, body, actions)
 }
+
+#[cfg(target_arch = "wasm32")]
+#[doc(hidden)]
+pub fn __diagnostic_to(d: &Diagnostic) -> crate::bindings::openidea::plugin::diagnostics::Diagnostic {
+    imp::diagnostic_to(d)
+}
diff --git a/sdk/rust/openidea-plugin/src/lib.rs b/sdk/rust/openidea-plugin/src/lib.rs
index 03c8e24a6..8518a3a4c 100644
--- a/sdk/rust/openidea-plugin/src/lib.rs
+++ b/sdk/rust/openidea-plugin/src/lib.rs
@@ -41,6 +41,7 @@
 
 pub mod commit;
 pub mod details;
+pub mod diagnostics;
 pub mod endpoints;
 pub mod file_actions;
 pub mod host;
@@ -160,6 +161,20 @@ pub mod semantic_bindings {
     });
 }
 
+#[cfg(target_arch = "wasm32")]
+#[doc(hidden)]
+pub mod diagnostics_bindings {
+    wit_bindgen::generate!({
+        world: "editor-diagnostics", path: "wit", pub_export_macro: true,
+        export_macro_name: "__export_diagnostics_world",
+        default_bindings_module: "openidea_plugin::diagnostics_bindings",
+        with: {
+            "openidea:plugin/types@1.3.0": crate::bindings::openidea::plugin::types,
+            "openidea:plugin/diagnostics@1.3.0": crate::bindings::openidea::plugin::diagnostics,
+        },
+    });
+}
+
 #[cfg(target_arch = "wasm32")]
 #[doc(hidden)]
 pub mod hover_bindings {
@@ -292,6 +307,9 @@ macro_rules! __optional_exports {
     (details, $plugin:ty, $component:ident) => {
         $crate::__details_exports!($plugin, $component);
     };
+    (diagnostics, $plugin:ty, $component:ident) => {
+        $crate::__diagnostics_exports!($plugin, $component);
+    };
     (hover, $plugin:ty, $component:ident) => {
         $crate::__hover_exports!($plugin, $component);
     };
@@ -533,6 +551,21 @@ macro_rules! __semantic_tokens_exports {
     };
 }
 
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __diagnostics_exports {
+    ($plugin:ty, $component:ident) => {
+        impl $crate::diagnostics_bindings::exports::openidea::plugin::diagnostics_provider::Guest for $component {
+            fn diagnostics(
+                doc: $crate::diagnostics_bindings::exports::openidea::plugin::diagnostics_provider::Document,
+            ) -> ::std::vec::Vec<$crate::bindings::openidea::plugin::diagnostics::Diagnostic> {
+                $crate::__rt::diagnostics::<$plugin>(doc)
+            }
+        }
+        $crate::diagnostics_bindings::__export_diagnostics_world!($component with_types_in $crate::diagnostics_bindings);
+    };
+}
+
 #[doc(hidden)]
 #[macro_export]
 macro_rules! __hover_exports {
@@ -820,6 +853,13 @@ pub mod __rt {
             .collect()
     }
 
+    pub fn diagnostics<T: Plugin + crate::diagnostics::DiagnosticsProvider + Default>(
+        d: crate::diagnostics_bindings::exports::openidea::plugin::diagnostics_provider::Document,
+    ) -> Vec<b::diagnostics::Diagnostic> {
+        let doc = crate::providers::Document { path: d.path, language: d.language, version: d.version, text: d.text };
+        with::<T, _>(|p| p.diagnostics(&doc)).iter().map(crate::host::__diagnostic_to).collect()
+    }
+
     pub fn hover<T: Plugin + crate::hover::HoverProvider + Default>(
         d: crate::hover_bindings::exports::openidea::plugin::hover_provider::Document,
         pos: b::types::Position,
diff --git a/sdk/rust/openidea-plugin/src/mock.rs b/sdk/rust/openidea-plugin/src/mock.rs
index 5b7967c7e..7d2d1b50e 100644
--- a/sdk/rust/openidea-plugin/src/mock.rs
+++ b/sdk/rust/openidea-plugin/src/mock.rs
@@ -110,6 +110,7 @@ struct State {
     answers: VecDeque<Option<Vec<String>>>,
     revealed_views: Vec<String>,
     diagnostics: BTreeMap<String, Vec<Diagnostic>>,
+    provider_diagnostics: BTreeMap<String, Vec<Diagnostic>>,
     secrets: BTreeMap<String, String>,
     net: Option<NetHandler>,
     requests: Vec<HttpRequest>,
@@ -362,6 +363,31 @@ impl MockHost {
         self.state.borrow().diagnostics.clone()
     }
 
+    /// Runs a diagnostics provider against the current mock editor snapshot.
+    /// This explicit call replaces the real host's debounce; it needs no capability.
+    pub fn refresh_diagnostics(&self, provider: &mut impl crate::diagnostics::DiagnosticsProvider) {
+        let document = self.state.borrow().editor.as_ref().map(|e| crate::diagnostics::Document {
+            path: e.path.clone(),
+            language: e.language.clone(),
+            version: e.version,
+            text: e.text.clone(),
+        });
+        if let Some(document) = document {
+            let items = provider.diagnostics(&document);
+            let mut state = self.state.borrow_mut();
+            if items.is_empty() {
+                state.provider_diagnostics.remove(&document.path);
+            } else {
+                state.provider_diagnostics.insert(document.path, items);
+            }
+        }
+    }
+
+    /// Diagnostics returned by the provider, separate from manual publishing.
+    pub fn provider_diagnostics(&self) -> BTreeMap<String, Vec<Diagnostic>> {
+        self.state.borrow().provider_diagnostics.clone()
+    }
+
     /// Views the plugin asked to refresh, in order.
     pub fn refreshed_views(&self) -> Vec<String> {
         self.state.borrow().refreshed.clone()
diff --git a/sdk/rust/openidea-plugin/tests/diagnostics_exports.rs b/sdk/rust/openidea-plugin/tests/diagnostics_exports.rs
new file mode 100644
index 000000000..869e869d7
--- /dev/null
+++ b/sdk/rust/openidea-plugin/tests/diagnostics_exports.rs
@@ -0,0 +1,45 @@
+//! Inspect real components, including the two full export-order fixture features.
+use std::collections::BTreeSet;
+use std::path::{Path, PathBuf};
+use wit_parser::WorldItem;
+
+#[test]
+fn diagnostics_registration_keeps_the_requested_interfaces() {
+    let path = std::env::var_os("OPENIDEA_DIAGNOSTICS_COMPONENT").map(PathBuf::from).unwrap_or_else(|| {
+        Path::new(env!("CARGO_MANIFEST_DIR"))
+            .join("../../../crates/ide-plugin/tests/fixtures/diagnostics/dist/plugin.wasm")
+    });
+    let wit_parser::decoding::DecodedWasm::Component(resolve, world) =
+        wit_parser::decoding::decode(&std::fs::read(&path).unwrap()).unwrap()
+    else {
+        panic!("expected a component")
+    };
+    let actual: BTreeSet<_> = resolve.worlds[world]
+        .exports
+        .values()
+        .filter_map(|item| {
+            let WorldItem::Interface { id, .. } = item else { return None };
+            let interface = &resolve.interfaces[*id];
+            let package = &resolve.packages[interface.package?];
+            (package.name.namespace == "openidea").then_some(interface.name.as_deref()).flatten()
+        })
+        .collect();
+    let mut expected = BTreeSet::from(["lifecycle", "commands", "event-handler", "diagnostics-provider"]);
+    if std::env::var_os("OPENIDEA_DIAGNOSTICS_COMBINED").is_some() {
+        expected.extend([
+            "endpoints-provider",
+            "view-provider",
+            "document-indexer",
+            "syntax-provider",
+            "semantic-tokens-provider",
+            "hover-provider",
+            "providers",
+            "inlay-hints-provider",
+            "detail-provider",
+            "commit-checker",
+            "file-actions",
+        ]);
+    }
+    println!("{} exports {actual:?}", path.display());
+    assert_eq!(actual, expected);
+}
diff --git a/sdk/rust/openidea-plugin/wit/diagnostics.wit b/sdk/rust/openidea-plugin/wit/diagnostics.wit
new file mode 100644
index 000000000..c3bf18130
--- /dev/null
+++ b/sdk/rust/openidea-plugin/wit/diagnostics.wit
@@ -0,0 +1,15 @@
+package openidea:plugin@1.3.0;
+
+/// Optional diagnostics for the current, possibly unsaved document (API 1.3).
+interface diagnostics-provider {
+    use diagnostics.{diagnostic};
+
+    record document {
+        path: string,
+        language: string,
+        version: u64,
+        text: string,
+    }
+
+    diagnostics: func(doc: document) -> list<diagnostic>;
+}
diff --git a/sdk/rust/openidea-plugin/wit/plugin.wit b/sdk/rust/openidea-plugin/wit/plugin.wit
index 2f8afeb49..d619cba19 100644
--- a/sdk/rust/openidea-plugin/wit/plugin.wit
+++ b/sdk/rust/openidea-plugin/wit/plugin.wit
@@ -152,3 +152,14 @@ world plugin-endpoints {
 world endpoints {
     export endpoints-provider;
 }
+
+/// A plugin with diagnostics under `[[contributes.providers]]`.
+world plugin-diagnostics {
+    include plugin;
+    export diagnostics-provider;
+}
+
+/// `diagnostics` is already the released host interface name.
+world editor-diagnostics {
+    export diagnostics-provider;
+}
diff --git a/src/features/plugins/__tests__/plugins.test.tsx b/src/features/plugins/__tests__/plugins.test.tsx
index e00827d27..f8f2ed50d 100644
--- a/src/features/plugins/__tests__/plugins.test.tsx
+++ b/src/features/plugins/__tests__/plugins.test.tsx
@@ -135,6 +135,15 @@ afterEach(() => {
 });
 
 describe("plugin actions", () => {
+  it("names manual and provider inspection producers after their plugin", async () => {
+    const { useProducerNames } = await import("@/platform/inspections");
+    usePlugins.setState({ plugins: [plugin({ id: "a", name: "Alpha" })] });
+    const stop = syncProjection();
+    expect(useProducerNames.getState().names.get("plugin:a")).toBe("Alpha");
+    expect(useProducerNames.getState().names.get("plugin-provider:a")).toBe("Alpha");
+    stop();
+  });
+
   it("projects command contributions to plugin.<plugin>.<command> actions", () => {
     const cmd = (pluginId: string, id: string, extra: Record<string, unknown> = {}) => ({
       pluginId,
diff --git a/src/features/plugins/bridge.ts b/src/features/plugins/bridge.ts
index 0a81aeb9a..a0fd057ce 100644
--- a/src/features/plugins/bridge.ts
+++ b/src/features/plugins/bridge.ts
@@ -53,7 +53,14 @@ export function syncProjection(): () => void {
     const s = usePlugins.getState();
     syncUiContributions(localizeContributions(s.ui, usePluginCatalogs.getState().catalogs), s.plugins);
     // Their problems are listed by name in Settings › Inspections.
-    useProducerNames.setState({ names: new Map(s.plugins.map((p) => [`plugin:${p.id}`, p.name])) });
+    useProducerNames.setState({
+      names: new Map(
+        s.plugins.flatMap((p): [string, string][] => [
+          [`plugin:${p.id}`, p.name],
+          [`plugin-provider:${p.id}`, p.name],
+        ]),
+      ),
+    });
   };
   const loadCatalogs = () => void loadPluginCatalogs(usePlugins.getState().ui, useI18n.getState().locale);
   apply();
diff --git a/wit/diagnostics.wit b/wit/diagnostics.wit
new file mode 100644
index 000000000..c3bf18130
--- /dev/null
+++ b/wit/diagnostics.wit
@@ -0,0 +1,15 @@
+package openidea:plugin@1.3.0;
+
+/// Optional diagnostics for the current, possibly unsaved document (API 1.3).
+interface diagnostics-provider {
+    use diagnostics.{diagnostic};
+
+    record document {
+        path: string,
+        language: string,
+        version: u64,
+        text: string,
+    }
+
+    diagnostics: func(doc: document) -> list<diagnostic>;
+}
diff --git a/wit/plugin.wit b/wit/plugin.wit
index 2f8afeb49..d619cba19 100644
--- a/wit/plugin.wit
+++ b/wit/plugin.wit
@@ -152,3 +152,14 @@ world plugin-endpoints {
 world endpoints {
     export endpoints-provider;
 }
+
+/// A plugin with diagnostics under `[[contributes.providers]]`.
+world plugin-diagnostics {
+    include plugin;
+    export diagnostics-provider;
+}
+
+/// `diagnostics` is already the released host interface name.
+world editor-diagnostics {
+    export diagnostics-provider;
+}